Max aperture on zoom lenses - stepwise or linear?

Question

When zooming with lenses without a fixed max aperture, the change in aperture* that the camera displays is stepwise, usually in steps of thirds. But, is the max aperture really the same all the way as long as the camera says it's the same, or is there a differense within the same steps? I.e, will the aperture actually be a little bigger at the widest end of such an interval?

And, are there any charts etc available that shows zoom lenses' intermediate max apertures, between longest and shortest focal length? I'm mostly interested in Canon, but other brands as well.

*) edit: I guess F-number is more acurate.

Asked by Daniero

Answer

The selected aperture is rarely the actual exact physical aperture of the lens. Usually there is a certain amount of discrepancy between the relative aperture the camera reports, such as f/3.5, and the actual physical area of the current aperture. As such, exposure is rarely exact, and can vary to a measurable (and often visible) degree between samples of a given lens and between a given lens and samples of a given camera. There are also often variations by as much as 1/3rd of a stop or more between camera brands for what would otherwise be exactly the same exposure settings with otherwise equivalent lenses.

The best real-world demonstrations of the difference between a reported aperture and the specification of aperture of a lens required to achieve its design are usually lens patents. Some recent Canon lens patents as reported by Canon Rumors are a great example of some real-world "relative aperture" values for pending lens designs:

Example 1
- Zoom ratio 4.01
- 135.50 – - 290.90mm 72.50 focal length
- Fno 4.66 -. 4.97 – 5.87
- 9.07 – - 4.25deg 16.62 a half angle of view.
- Image height 21.64mm
- 171.47 – - 204.08mm 144.08 full-length lens
- BF 40.08mm
- 18 sheets 12 group lens configuration
- 3 UD glass sheet
- A plane diffraction
- Seven-group zoom positive and negative positive positive and negative polarity
- Inner Focus (Group 6)
- Shake correction (group 2)

Example 2
- Zoom ratio 2.84
- 200.00 – - 292.50mm 103.00 focal length
- Fno 4.67 -. 5.44 – 5.77
- 6.17 – - 4.23deg 11.86 a half angle of view.
- Image height 21.64mm
- 189.12 – - 210.66mm 162.16 full-length lens
- BF 45.16 – 58.25 – 70.16mm
- 13 pieces in 11 groups Lens Construction
- 2 UD glass sheet
- A plane diffraction - Five-group zoom of positive and negative positive positive and negative
- Rear focus

You'll notice the Fno specifications for these two examples of new DO or diffractive optics lens designs. The first example lists the F-Number range as 4.66 to 5.87. Neither of those are standard F#'s, such as f/4.5, f/5 or f/5.6, however they are the specified engineering limits of the lens. You can't actually dial in an exact f/4.5 aperture on Example Lens #1...when you do, you are actually getting an actual f/4.66 aperture. Same deal if you dial in f/5.6, which in reality would mean your getting an actual aperture of f/5.87. (The middle aperture number, if I understand the rather oddball nomenclature of these patents, would be what you get around the middle of the lens, which seems to be the first focal length number, which in the case of Lens #1 is 135mm.)

As you change the focal length of a lens at maximum aperture for a variable aperture lens, the physical size of the aperture DOES NOT change. The diaphragm remains at its widest-possible ("relaxed") setting. The real F-Number's will change smoothly and not in a non-stepped manner. The lens will report the nearest "well-known" 1/3rd stop aperture at one of the specified points (i.e. f/4.5 for f/4.66 @ 72.5mm, f/5 for f/4.97 @ 135.5mm, f/5.6 for f/5.87 @ 290.9mm), and that is what will show up in EXIF as the selected aperture, however the actual apertures (i.e. f/5.87) will often show up in EXIF as "Max Aperture Value" or something similar.

You can usually observe this smooth change in aperture if you point a lens up towards your face with a bright light above your head so it illuminates the inner barrel of the lens, and adjust the focal length. You will see that the camera does not do any kind of micro-adjustment of aperture for you as you zoom. This is always the case at maximum aperture, and usually the case at all other apertures, although sometimes there are slight differences between instances of stopping the lens down to a smaller aperture simply due to the nature of a diaphragms operation. (Use a DOF Preview button to see the behavior at any aperture, including max aperture...otherwise the camera will always remain in a "relaxed" state.)

The same precision differences are present in other aspects of the lens as well. Example Lens #1 is actually a lens with a zoom ratio of 4. Funky nomenclature aside, the lens is actually a 72.5mm to 290mm lens...or a replacement for the 70-300mm f/4.5-f/5.6 DO lens. Similarly, Example Lens #2 is actually a 100-300mm f/4.5-5.6 DO lens.

While these imprecise specifications, at least relative to the idealistic numbers we photographers usually think about, are actually very exact and very necessary to the successful manufacture of a given lens at a given price point. Lens manufacture for DSLR lenses is very complex, and particularly when you get into larger lenses or extremely wide angle lenses, can be very costly due to the physical size of many of the necessary lens elements. Diffractive Optics (DO) lenses have the added complexity of diffraction-grating elements that, while they allow lenses to be made physically smaller, require an extra set of complex manufacturing procedures.

Precise specifications like this allow manufacturers to create a 100-300mm DO lens they can actually sell and make a bit of a profit on, without the discrepancies with their "sales specifications" (i.e. 103mm - 292.5mm rather than a lens that is exactly 100mm - 300mm) really having much of a difference in real-world user. It should be noted that these discrepancies really do not matter in the real-world, and the discrepancies can be larger at longer focal lengths. Some ten millimeters or so difference at supertelephoto lengths, a few millimeters of difference at normal to short telephoto lengths, or a fraction of a millimeter at wide-angle lengths, as well as small discrepancies in F-Number are all indistinguishable by photographers in the real world, so don't let them bother you.

Answered by jrista

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What is the technical difference between focus and zooming?

Question

This may look like a silly question but I don't know what the difference between zooming and focusing is. Zooming in will usually let me have fewer subjects in the scene while zooming out will allow for wider view. Focusing is the process adjusting the wanted subject to be in focus and look sharp. When we zoom, lens elements are moved to zoom in or out, what happens in the lens when we change the focus?

Asked by Akram Mellice

Answer

The two generally control two different aspects of the image projected by the lens. Focusing sometimes has the effect of changing "zoom" a little as well, however its purpose is different. To keep it simple:

• Focus adjusts the Focal Plane
  • The focal plane is the thin plane of reality that is focused clearly on the imaging medium
  • Focusing moves this plane nearer or farther from the camera's sensor/film
• Zoom adjusts the Angle of View
  • The angle of view is the breadth of the scene projected by the lens
  • Wide-angle lenses tend to capture very broad scenes (large angle of view)
  • Telephoto lenses tend to capture very narrow scenes (small angle of view)

Focusing in the past used to be achieved by moving the lens itself (i.e. in a large-format view camera) forward or backward (away/towards the imaging medium). This often results in changes to the angle of view as well, since the total focal length of the lens can change via extension...sometimes by a lot. In modern camera lenses, focusing may be achieved similarly...many cheap lenses focus by moving the front or back (or both) lens elements. Higher quality lenses tend to use an internal floating focus group, an internal group of lens elements who's sole purpose is to focus the image. The benefit of internal focusing groups is that the physical length of the lens stays the same, allowing you to minimize the amount of "zoom shift" that might occur when focusing.

Answered by jrista

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What are the differences between the Canon EF 70-200mm f/2.8L IS II USM lens and the one that isn't IS II?

Question

On Amazon, the Canon EF 70-200mm f/2.8L IS II USM Telephoto Zoom Lens for Canon SLR Cameras is $2500 whereas the Canon EF 70-200mm f/2.8L USM Telephoto Zoom Lens for Canon SLR Cameras is a mere $1400. Why is there such an important price difference? I'm saving to buy the cheaper one; should I wait, save more money and buy the "better" one?

Asked by the.midget

Answer

Adding to to the answer above it has to be mentioned that a zoom lens benefits significantly from the Image stabilizer. I own the IS lens and can tell you that the effect is very strong, specially if you use a 1.4 or higher extension on the lens.

The price difference is given by the fact that the non-IS lens you listed here is much older (its the first, not the II model) AND lacks the image stabilizer. You should read reviews of all 4 lenses (IS vs. non-IS, I vs II) To see how big the quality difference is and if it matters to you. If you look for example at the lens flare comparison, the older lenses perform MUCH worse than the new ones, similar for contrast.

In general, I can only recommend to never save on a lens, specially the L lenses since they last for a very long time and are more important than having a good camera in my opinion. You will change bodies over the years more often than throwing out a lens and getting the successor model.

Answered by uncovery

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Why is the Canon MP-E 65mm F/2.8 Macro Lens not called a zoom?

Question

The Canon MP-E 65mm works differently than my other macro lenses. Compare:

• With a standard 35mm macro, I can frame first and then adjust focus which only changes framing very slightly with.
• With the MP-E 65mm changing focus completely changes framing.

Assuming that the angle of view corresponds to a 65mm lens at 1X magnification, it seems that by 5X, the angle of view is about that of a 325mm lens! In other words, manual focusing (this lens does not autofocus at all) looks like it has the same effect as zooming on a zoom lens with the plane of focus fixed at the closest focus-distance.

So why is this not called a MP-E 65-325mm instead of simply 65mm? More importantly, what does the 65mm focal-length represent? And how can I use that to frame by shots with less guesswork?

Asked by Itai

Answer

It's called a 65mm because that's the combined focal length (light bending ability) of the lens elements. The focusing mechanism on the MPE-65 works like a set of bellows, i.e. it just moves the whole lens back and forth. You can see this as the physical length of the lens barrel changes significantly when focusing. This has the effect of changing both the minimum focus distance and the angle of view, however the focal length of the lens elements remains unchanged.

It's common for prime lenses change field of view slightly on focusing, the effect is just exaggerated with the MPE-65. Lots of rules break down when you get into macro and super-macro photography, focal length, f-stop etc. cease to matter as the formulas for things like depth of field and exposure don't give accurate answers at macro distances. You have to ignore what it says on the lens and use your judgement or trial an error to begin with.

Note it's standard practice to state the focal length of a lens when focussed at infinity (to account for minor variations as mentioned above). As the MPE-65 doesn't focus to infinity I assume they measure it for the 1x setting, so the value is not directly comparable with other lenses.

Answered by Matt Grum

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Canon EF-S 15-85mm IS USM or Canon EF-S 18-135mm IS to replace a broken kit lens?

Question

I'm looking to upgrade the 18-55 kit lens I got with my 450D. I finally settled choosing between these two.
Which one would you get and why?

I do mostly amateur photography on my spare time, trips and family events. I also have a Canon 55-250 zoom lens I take with me sometimes to complement the 18-55.
The 15-85 is appealing since it would stretch the range I currently have and it feels slightly more high-end
The 18-135 on the other hand has the appeal that if I don't feel like taking the zoom lens, I can still get a pretty good range.

What would you do?

Asked by shoosh

Answer

Assuming you have the budget for the 15-85mm (almost twice the price of the 18-135mm) I'd recommend the 15-85mm lens over the 18-135mm. Why?

• It has better reach on the wide angle which you wouldn't be able to cover with your 18-135mm + 55-250mm combo. A lot of lenses cover up-to 85mm but none of them goes down to 15mm.
• It has better image quality and able to render very good colors.
• It's sharpness is comparable to any L grade lens, on the other hand, the 18-135mm is much softer.
• It has Canons top of the line USM focus motor, which is faster and quieter. The 18-135mm doesn't have USM and makes sound while focusing.
• It has non rotating front element and also the focus ring doesn't rotate while focusing, a automatic choice for filter users. The 18-135mm also has a non-rotating front but the focus ring moves during AF.
• It provides FTM (full time manual focus), handy feature for fine-tuning or doing focus adjustments quickly.
• It's build quality is better and also has focus distance meter.

ISO 12233 Chart 100% crop comparison between the 15-85mm and the 18-135mm, please refer to this link. Compare at different focal lengths and see the difference for yourself.

Overall, the 15-85mm is a better built, better performing and better featured lens comparing to the 18-135mm in almost every aspect. It also weighs more, costs more and having a larger filter thread (72mm over 67mm) makes the filters expensive. Once you get used to the quality this lens provide, you might even consider replacing your 55-250mm lens with may be a 70-200mm f/4 (mayybe) ;)

Answered by ShutterBug

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Canon EF-S 15-85mm IS USM or Canon EF-S 18-135mm IS

Question

I'm looking to upgrade the 18-55 kit lens I got with my 450D. I finally settled choosing between these two.
Which one would you get and why?

I do mostly amateur photography on my spare time, trips and family events. I also have a Canon 55-250 zoom lens I take with me sometimes to complement the 18-55.
The 15-85 is appealing since it would stretch the range I currently have and it feels slightly more high-end
The 18-135 on the other hand has the appeal that if I don't feel like taking the zoom lens, I can still get a pretty good range.
What would you do?

Asked by shoosh

Answer

Assuming you have the budget for the 15-85mm (almost twice the price of the 18-135mm) I'd recommend the 15-85mm lens over the 18-135mm. Why?

• It has better reach on the wide angle which you wouldn't be able to cover with your 18-135mm + 55-250mm combo. A lot of lenses cover up-to 85mm but none of them goes down to 15mm.
• It has better image quality and able to render very good colors.
• It's sharpness is comparable to any L grade lens, on the other hand, the 18-135mm is much softer.
• It has Canons top of the line USM focus motor, which is faster and quieter. The 18-135mm doesn't have USM and makes sound while focusing.
• It has non rotating front element and also the focus ring doesn't rotate while focusing, a automatic choice for filter users. The 18-135mm also has a non-rotating front but the focus ring moves during AF.
• It provides FTM (full time manual focus), handy feature for fine-tuning or doing focus adjustments quickly.
• It's build quality is better and also has focus distance meter.

ISO 12233 Chart 100% crop comparison between the 15-85mm and the 18-135mm, please refer to this link. Compare at different focal lengths and see the difference for yourself.

Overall, the 15-85mm is a better built, better performing and better featured lens comparing to the 18-135mm in almost every aspect. It also weighs more, costs more and having a larger filter thread (72mm over 67mm) makes the filters expensive. Once you get used to the quality this lens provide, you might even consider replacing your 55-250mm lens with may be a 70-200mm f/4 (mayybe) ;)

Answered by ShutterBug

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Does image quality on compact cameras degrade when zooming in?

Question

I have a Panasonic Lumix LX5 which I find generally produces good photos. However I have noticed on numerous occasions that the image quality when at the limit of the optical zoom (not using the digital zoom) seems to be lower (more grainy/blurry). Is this most likely to be effects like camera shake, or even atmospheric pollution, or is it technically possible that the lens isn't as sharp at full zoom? What would be the best way to test this theory out?

EDIT:

Updated following the suggestions to include a couple of 100% crops plus the original resized.

Original Image (resized)

1st 100% crop

2nd 100% crop

Asked by mdresser

Answer

The problem is probably multifaceted.

You mentioned that the image was more grainy at the limit of the optical zoom. The LX5 has a variable aperture, from f/2.0 down to f/3.3, which would mean you either need a slower shutter speed or a higher ISO to compensate. If you use a lower shutter speed, its more likely that you'll introduce camera shake, and if you use a higher ISO you'll introduce more noise. If you shoot at a lower ISO and force a longer shutter, you could get camera shake, and also need to increase the brightness in post, which would again increase noise (probably making it worse than if you just used a higher ISO to start with.)

Finally, while the lens on that camera is good, all zooms have to make compromises. Its entirely possible that its a little soft at the extremes (or one or the other extreme), as its impossible to make a zoom lens cost effective and also maintain prime-level IQ.

I can't say specifically if you actually have any issue, or what it may be, without seeing some sample shots. If you added 100% crops as well as scaled down full photos, it would help us determine if what you are seeing is simply the result of pixel-peeping, and therefor something you could ignore...or a true problem.

EDIT:

Based on the sample images that were added, I can't say I see any serious quality issues. For one, there are some compression artifacts, and thats just something you can't get away from with JPEG. Second, the lower detail in the distance is a combination of atmospheric haze eating away detail before it even gets to the camera, and the simple fact that its off in the distance...only so much the lens in the LX5 can do to resolve detail that far away. The foreground detail looks pretty good, so I wouldn't worry about anything.

Answered by jrista

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How much different are the Tamron 17-50mm f/2.8 stabilized (VC) and non-stabilized versions?

Question

I have seen these 2 lenses being suggested by many people across the site as general purpose zooms and an upgrade to the typical 18-55mm kit lenses. The price difference seems to be around $200 (~INR 10,000) between the two. The lenses are also considerably cheaper than their Canon\Nikon counterparts.

Having using the stabilized kit lens on Canon, I appreciate the importance of IS\VC for slow shutter speeds (not just low light, but also for effects). However, quite a few reviews seem to suggest that the non-VC version seems to be better optically overall. There seem to be more quality control issues with the VC version as well.

My question is two fold:

1. How do the 2 lenses compare against each other - is the premium for the VC version worthwhile for the quality trade-off?
2. How do the 2 compare to the Canon stabilized kit lens (EF-S 18-55mm IS) in terms of optical quality - are they worthwhile upgrades? (there is a similar question for Nikon)

Answer

I have the VC version (Nikon mount). I have tested it alongside my 50mm prime and found it to be just as sharp at f/3.2. It is very slightly softer at f/2.8, but only when looking at an artificial test pattern. That's one person's opinion based on a sample of one.

I have tested other non-professional zoom lenses (Nikon and Sigma) and the Tamron is far, far sharper than any of them. Unbelievably so.

A camera shop owner I know recommended the non-VC version as being very sharp and reliable (and inexpensive). He didn't say it was worth buying the non-VC version over the VC version. He just recommended it highly as a fantastic value. He did say he'd also sold a lot of the VC version and hadn't noticed any quality control issues.

Because the lens is sharp wide open, VC isn't really vital except in low light. I would say the VC is probably not worth the premium unless you intend to shoot a lot of low-light or indoors work without flash.

Can't help with the comparison to the Canon 18-55mm. I would imagine from what I've found compared to other Nikon equivalents that the Tamron will be noticeably sharper, especially wide open. You can use it at 2.8 or 3.2, whereas the Canon probably needs to be stopped down to f/5.6 or f/8 to be at its sharpest.

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Why does my aperture setting change as I zoom the lens on my Nikon D90?

Question

I am new to the photography field and this something which I am not able to understand. I am playing around with my Nikon D90 along with its kit lens (18-105mm).

While reading about Depth of preview, the author asks to do some basic exercise to better understand DOF, like this:

• set your aperture to smallest number f/2.8, f/3.5, f/4 with 70mm or longer lens.

When I tried to set aperture to f/3.5, and tried to change focal length, my camera is setting aperture automatically in every every possible mode (which I know of). It is changing aperture in the following fashion:

1. 18-24 ----> 3.4 to 4
2. 18-35 ----> 4.5
3. 18-50 ----> 5
4. 18-105 ---> 5.6

But if i set my aperture to 5.6 or higher, it does not change when I change the focal length of my camera. I know I am not doing some basic thing right, but I'm still not sure why this is happening. Might some one help me to understand this?

Answer

It is happening because you have a variable aperture zoom lens. The solution is to get a quality lens, otherwise you have to live with the limitations which are actually marked on the barrel of your lens.

It says 18-105mm 1 : 3.5 - 5.6G which means your maximum aperture is F/3.5 at the widest focal-length (18mm) and F/5.6 at the longest (105mm). It changes in increments between that. So, if you are set to F/5.6 then you can zoom with whole focal-length without aperture changing. If you set your aperture to F/3.5 then after a short increase in focal-length, the lens has to diminish its aperture.

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How important is optical zoom in snapshot cameras?

Question

I want to buy a new snapshot camera. Because i want a new one with geo-tagging, I haven't such a great choice. So the following three cameras are my favorites:

http://digitec.ch/ProdukteVergleichen1.aspx?artikel=209007,207072,208802

• Canon Powershot SX230 HS
• Sony DSC-HX7V
• Panasonic Lumix TZ20

But now they look all very similar to me. The biggest difference I can see as a beginner is the optical zoom. Is this correct? Or is there a more important difference that I can't see?

And if it is only the optical zoom. How much is the difference between 10x and 16x? Do I feel any difference?

Answer

I never tried to hold a 384e mm zoom on such a camera, but as @dpolitt mentioned it might be very difficult. You may want to try that at a store or read up on that.

But, leaving any other image quality aspects aside, I think the wide angle focal length might be much more interesting. 24e to 28e mm, from your given comparison, is quite a difference which cannot be compensated by moving your feet as much as on the narrow angle end. If that is important to your needs, of course.

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Why push/pull zoom is not widespread?

Question

The Canon EF 100-400mm f/4.5-5.6 L IS USM has a push/pull zoom mechanism instead of a zoom ring. Other lenses, like the Nikon 80-200mm f/2.8 AF released in 1988 use this type of zoom too, but the lenses with a push/pull zoom are very rare (none among today Nikkor lenses, I believe).

This zoom seems ways more practical and it is especially much faster to move the front element instead of rotating the ring. The possible issues like the lens extending or collapsing when pointed to the sky or to the ground are solved by the tension ring¹.

Why is this not widespread on pro telephoto lenses? What are the drawbacks? Is the only reason to avoid to move/rotate the front element because of the air flow?

---

^{¹ In Canon EF 100-400mm f/4.5-5.6 L IS USM, the tension ring is close to the focus ring, which makes it easy to move the wrong ring by mistake, but this particular issue is related to the lens itself and not the push/pull zoom mechanism, so it's out of scope of this question.}

Answer

Not speaking for any company/lens designer, but I think it's a lot less practical now than it was in the manual focus days when one hand on one ring controlled both zoom and focus. The push/pull zoom was less precise than a rotating ring (it took some small force to move from any rest position, so overshooting was easy for critical composition), but managing everything from a single ring made life simpler overall.

But to extend the question a bit: why did push/pull focus fall from grace? After all, for a unit-focus lens (a lens where all of the elements/groups are in a fixed relationship with one another, and the whole assembly is moved toward or away from the film/sensor as a unit), that's all you need (and you can, if you wish, use push/pull focus alone on most rail-type view cameras). Two things make it impractical -- a lack of precision on the one hand, and the fact that lenses on small-format cameras don't tend to be unit-focus these days (internal focus, which is actually a sort of zoom, and corrective elements that float in relation to the rest are closer to the norm these days).

With focus largely outsourced to the camera, the more precise two-ring arrangement is a lot less annoying than it used to be (like on my old Minolta 35-70mm f/3.5MD). With focus control being mostly a matter of a button-push with the right hand, the left hand is free to concentrate on the zoom. With a ring, the only real annoyance is backlash -- there's usually a small but detectable "dead period" -- just the tiniest fraction of a degree -- when you reverse the direction you're rotating the ring. With a push/pull, on the other hand, there's usually some stuttering as you overcome the friction (the "tension ring"), so making fine adjustments after you've done the gross positioning is sometimes difficult and frustrating. You might think that really, really small adjustments aren't nearly as critical as a lot of people think they are (and I'd be inclined to agree with you), but as long as photographers are convinced that they have no pixels to waste at all, precision is going to win out over speed as long as the speed penalty isn't outrageous.

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When you zoom in with a lens on an SLR why does the lens go in then out?

Question

I guess this is more a question of optics than photography but I just got an SLR with a basic 18-55 lens. I noticed that when going from 18 to 55 or 55 to 18 the lens physically comes back in and then physically goes back out?

What is going on there? I would think that if I am zooming in the lens should be going out 100% of the time but the lens actually goes out and then comes back in.

Answer

The lens is retrofocal at the wide end and telephoto at the long end. A retrofocus lens is referred to as "inverted telephoto" because it is constructed similarly to a telephoto lens with the elements reversed. The effect decreases as you zoom in, until you reach about 35mm, at which the lens begins to extend and eventually becomes a telephoto configuration, where the size of the lens, front element to rear element, is less than the focal length. The lens is neither retrofocal nor telephoto between these positions. This results in the lens being longer at the extremes of the zoom range than at intermediate positions.

For more information on this design, see the Wikipedia articles on Angénieux retrofocus, which discusses the origin of the design for the wide end, and telephoto lens for what happens at the long end. According to the telephoto lens article:

Zoom lenses that are telephotos at one extreme of the zoom range and retrofocus at the other are now common.

This is essentially what is happening with your 18-55mm lens. As far as I am aware, Canon, Nikon, Pentax, and Sony (A-mount, not E-mount) 18-55mm lenses all share this design aspect.

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Will a prime lens help me get better portraits at a wedding?

Question

I have a Canon 600D with the EF-S 18-55mm f/3.5-5.6 IS lens. I have a friend's wedding coming soon, and I'm not sure if my zoom lens will do a good job or not. I was thinking of buying a prime lens so I can get better portraits, but I'm not sure if this is true.

The wedding will be in a hall with different light situations (sometimes it's bright, sometimes it's dark, and they'll use laser lighting a lot), there is a garden associated with the hall, and the wedding will be at night. I'm not the official photographer for the event.

Answer

Prime lenses are excellent options for portrait work, especially at wedding venues. Prime lenses are less forgiving when it comes to varied situations and framing. Instead of moving the zoom ring, you have to move your feet. If you are the main photographer for an event, no one is going to mind you moving around to get the shot. If you are an audience member attending the wedding as a guest, it may be considered rude to get move around so much for a shot.

Typically indoor weddings have poor lighting, at both the ceremony and reception events. Because of that, fast lenses of at least f/2.8 are usually the standard. You could fill your gear bag with zoom lenses at f/2.8, and shoot weddings very well, but it would likely be less expensive to purchase a few f/1.4, f/1.8 or f/2.0 lenses that are wider yet.

Another benefit of prime lenses is that typically they are smaller and lighter then a professional grade zoom lens.

For portraits specifically, a wider aperture will provide you with a more blurred background, referred to as bokeh. It also will let you stop action such as a moving bride or groom, and allow you to use a lower ISO setting if you are worried about noise.

Overall, prime lenses are a great option for wedding photography, because they are particularly good at portrait work, especially in low light.

To get started these questions may help you with your first purchase:

• Is it worth it to have the 50mm f/1.8 Canon lens?
• Is a 50mm f/1.8 or 50mm f/1.4 a good lens for portraits in low light?

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Why do zoom lenses and compact cameras have varied maximum aperture across the zoom range?

Question

Why does a camera's maximum (allowed) aperture get smaller when you increase its zoom?

Answer

The short answer is because it is cheaper to manufacture such lenses. The longer the lens and the wider the aperture, the larger the optical elements in the lens - thus larger the expense to produce them.

A lens like 70-200/2.8 must have a front optical element of 200mm/2.8=72mm, which is quite a chunk of glass. On the other hand, the 70-300/4-5.6 needs to be 300mm/5.6=54mm wide. If it were f/4 through its full range, the optical element would need to be 75mm wide - even larger than the much more expensive 70-200/2.8.

In your question, you say "the camera's maximum aperture". The camera does not have an aperture - the lens does. Minor but important difference, especially for SLRs - once you remove the lens you see that the camera is just a light bucket with a big hole in the front.

DETAILS:

The aperture is the ratio of the focal length of the lens to the size of the front optical element. Essentially

aperture = focal length / optical element size

For example, a 50mm f/1.8 lens has a 28 mm (50/1.8) element size.

If you're wondering why the f-stop numbers don't seem to be linear (they're not), it is because the amount of light collected by the lens is proportional to the focal length divided by the aperture. Because of this power of 2, f/4 collects twice as much light as f/5.6, since 5.6/4=sqrt(2).

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What are particular potential problems to watch for when using a telephoto zoom?

Question

I recently got the Canon EF-S 55-250mm IS II lens as a complement to my 18-55mm kit lens for my 550D. I was looking for some advice\best practices for using a telephoto zoom, any associated accessories like hoods that would be useful and any gotchas that I should watch out for. My intended usage for the lens is to shoot stage shows and portraits.

I found a similar query for Point & Shoot cameras

Background

I decided to buy this lens based on the advice to an earlier question I had asked. The lens is fairly light for a telephoto zoom (~400g), and not too large either. However, it is considerably longer than the kit lens. One of the main reasons I picked up this lens was to understand the longer focal lengths better without investing in a high end lens right away (photography is a hobby).

The 70-200mm f4 L IS was one lens I did consider, but that was in a different league - both in terms of price\quality and size\weight. I wish to explore the longer focal lengths before I make serious investments on pro quality lenses - zooms or primes.

Answer

Main thing you have to be careful with is to make sure your shutter speed is high enough for the longer shots to limit blurring due to camera shake. The rough rule of thumb here is it should be at least 1/n of a second where n is the focal length with IS turned off; note this would be the effective focal length so for a crop body you have to apply the crop factor of 1.6 for Canon. With IS on it gets you maximum 3 stops reduction in this but in my experience you should only ever really halve it. One thing to note about IS is that it takes a little time to settle down after activation so when you take a shot half press the shutter button then pause for a second before taking the shot to let the IS settle down.

Outdoors its always a good idea to use a hood because on bright days it lowers the chance of lens flare and also protects the end of the longer lens from hitting things; it does happen and a damaged hood is easier/cheaper to fix than damaged glass. For indoor work extra focal length gives you a lot of possibilities but with a slower lens like this you will have to pay particular attention to lighting. This is why pro photographers go for faster and way more expensive glass like f/2.8 because it makes lighting less of a concern.

Best thing to do is just start using it as it will take you a little time to get used to the weight and balance of the new lens on your camera.

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How to use a telephoto zoom?

Question

I recently got the Canon EF-S 55-250mm IS II lens as a complement to my 18-55mm kit lens for my 550D. I was looking for some advice\best practices for using a telephoto zoom, any associated accessories like hoods that would be useful and any gotchas that I should watch out for. My intended usage for the lens is to shoot stage shows and portraits.

I found a similar query for Point & Shoot cameras

Background

I decided to buy this lens based on the advice to an earlier question I had asked. The lens is fairly light for a telephoto zoom (~400g), and not too large either. However, it is considerably longer than the kit lens. One of the main reasons I picked up this lens was to understand the longer focal lengths better without investing in a high end lens right away (photography is a hobby).

The 70-200mm f4 L IS was one lens I did consider, but that was in a different league - both in terms of price\quality and size\weight. I wish to explore the longer focal lengths before I make serious investments on pro quality lenses - zooms or primes.

Answer

Main thing you have to be careful with is to make sure your shutter speed is high enough for the longer shots to limit blurring due to camera shake. The rough rule of thumb here is it should be at least 1/n of a second where n is the focal length with IS turned off; note this would be the effective focal length so for a crop body you have to apply the crop factor of 1.6 for Canon. With IS on it gets you maximum 3 stops reduction in this but in my experience you should only ever really halve it. One thing to note about IS is that it takes a little time to settle down after activation so when you take a shot half press the shutter button then pause for a second before taking the shot to let the IS settle down.

Outdoors its always a good idea to use a hood because on bright days it lowers the chance of lens flare and also protects the end of the longer lens from hitting things; it does happen and a damaged hood is easier/cheaper to fix than damaged glass. For indoor work extra focal length gives you a lot of possibilities but with a slower lens like this you will have to pay particular attention to lighting. This is why pro photographers go for faster and way more expensive glass like f/2.8 because it makes lighting less of a concern.

Best thing to do is just start using it as it will take you a little time to get used to the weight and balance of the new lens on your camera.

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Would a fixed or zoom telephoto lens be better for learning?

Question

My daughter has a Nikon D-90 camera body and two prime f1.4 lenses 50mm and 35mm. She is interested in learning more, and I am curious which of a zoom or fixed telephoto lens would help her best? Is getting a low f-stop lens important in a telephoto lens?

Answer

It depends on where she's feeling the limitations. I have a kit made up of 15mm, 40mm, and 70mm prime lenses (on a dSLR with the same 1.5× format as the Nikon D90), and for me, that's just about right. (I'd probably trade the 40mm for a 35mm were I starting over — tough call.) For my style, I don't miss having a zoom at all.

Since she has (and is presumably comfortable with) two prime lenses, she may feel the same way, and would just like to increase the range of focal lengths she has available. For that, another prime covering either wider-angle or more telephoto would fit nicely.

On the other hand, she might want to explore the convenience of a zoom. Having flexibility of framing can remove one-more-thing-to-worry-about from the learning process, and remove the potential need to switch lenses in the middle of the action.

Back on the first hand, though, there is a school of thought which argues that prime lenses have inherent advantages for learning composition. Mike Johnston's Case Against Zooms articulates this view well. The idea is that by learning to know a particular prime lens's inherent viewpoint, that limitation actually becomes a freedom.

Since I use my 40mm most often, I can attest to this: having used it to take thousands of photographs over the course of several years, I can know what photo my camera will make without having to actually put it to my eye. That's very useful, and helps me concentrate on taking the photographs I want to take with the view I want to have.

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How can a lens like a 18-55mm have more than one focal length?

Question

How can a lens have a range of focal lengths? Shouldn't it be a single number?

Isn't focal length supposed to be fixed for a lens of a particular shape and geometry?

What am I missing?

How many lenses are actually there in a "lens"?

Answer

A range of focal lengths indicates a zoom lens. There are two major classes of lenses. Primes, or primary lenses, have a single focal length. They tend to be higher quality, as there can be fewer lens elements, and fewer moving element groups. One exception to this rule is super telephoto prime lenses, particularly faster lenses (f/2.8), which are some of the most advanced optics on earth, and contain numerous element groups with special types of lens elements (i.e. ultra low dispersion glass, fluorite lenses, aspherical elements, etc.)

The other class are zoom lenses, and they have a range of focal lengths. They generally have more element groups overall, and usually have several moving groups. The length of a zoom lens can be increased or shortened, thus changing the focal length. The quality of a zoom lens depends on its construction. Some have great quality at one end of the range, and lesser quality at the other end. Some have great quality at the ends of the focal range, but lesser quality in the center of the range. Super telephoto zooms also often have special types of lens elements.

To answer the question about "how many lenses are in a lens", the question depends. Some lenses have few lens elements (individual glass or other material lenses within a camera lens body), and others have many. The number of lens elements in a given lens is usually an indication of a few things. Lower quality lenses tend to have fewer elements, and the glass used in those elements tends to be of a lower quality (less dense, greater chance of splitting light and causing things like chromatic aberration.) Lower-end lenses may have 3-5 lens elements total. Higher quality lenses tend to have more elements, and often larger elements. Many high-end lenses tend to have more lens elements, around 5-10. Higher end telephoto lenses may have 14-20 lens elements or more. More glass is generally required to produce wider apertures, and having a very wide front lens element often requires additional lens elements to focus that light down to a size that can pass through the lens mount into your camera. As focal length increases, maintaining the quality of the generated image often requires additional elements that serve different purposes. High end telephoto lenses often contain aspherical elements, ultra-low dispersion elements, fluorite elements, movable element groups, etc. These additional lens elements increase the control the lens has over light, but also increase the overall weight of the lens, and its manufacturing complexity.

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What features really matter in a point and shoot camera?

Question

I am planning to buy my first new digital camera. Now I am too confused for more than 20 days about how I can choose a camera.

I want to use the camera for domestic purpose.

The Canon IXUS 220 HS looks good but it is only 12 MP and only 5X zoom. But there is a also the Canon A3300 that is 16 MP.

So I don't know what is the basis of selecting a camera. What is Image Stabilization? When should I buy a CMOS sensor camera? How much Optical Zoom is sufficient? How much does noise matter in the camera?What about if the camera has HD video recording, and if not, how much will that lack affect viewing on my 32 inch TV?

The cameras I'm currently looking at are Nikon s3100, Canon IXUS 220 HS, Canon IXUS 110 HS, Canon A3300, and Sony W370/B. This will be my first camera and I can't take any risk because I cannot afford a new one in the next few years.

Answer

I would put the number of megapixels at the bottom of the priority list. Megapixels matter, but once you get past about 10 you'll have enough for anything you're likely to do. In particular there wont be a noticeable difference between 12 and 16, theoretically you'll be able to print a 16MP image 15% larger, but that's only if the lens resolves more detail and that detail is not lost to noise.

Image stabilzation prevents blur due to camera shake when you take a photo. It becomes very important the longer the zoom lens. With a 5x it's probably not important but once you get 10x or more you should definitely look for a stabilized model. How long a zoom you need is really up to you.

All small sensor point and shoot cameras will produce noisy images in low light, it's just something you need to be aware of and plan your shooting accordingly.

HD video is a useful feature, I've seen some really good quality clips from this sort of camera, so if you plan to take videos at all I'd look at one that records HD.

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Is it normal for a Nikon lens to make noise when zooming in or out?

Question

I read a lot of reviews when buying Nikon D5100 but no where did I hear this. Check this video on youtube. When you zoom in/out you can clearly hear the lens itself. This is highly undesirable. Is it normal with any DSLR or with Nikons only? Is this a genuine flaw? Canon Guys, do you hear this zoom as well?

Answer

Noises on the camera, such as the zooming of a lens or even an IS/VR motor, are often picked up by on-camera microphones. That's the disadvantage of an on-camera microphone and isn't specific to this camera or the Nikon brand.

The solution is to use a better mic that's either mounted off-camera or is a shotgun-style mic on the hotshoe where it won't pick up camera noise.

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