How does a short flange back distance improve image quality?

Question

In the description for the new lens mount for their X-Pro series, Fujifilm says:

1: Specifically designed to maximize the mirrorless design of the body, the X-Mount has a short flange back distance of just 17.7mm. This means the rear lens elements are as close as possible to the sensor. The wide opening allows the lens to be mounted deeper within the body - up to 7.5mm (approx) from the mount surface - reducing the back focus distance of each lens to the minimum possible, thus achieving high resolution all the way to the edge of the image.

How does this shorter-than-usual distance help "achieve high resolution"? Does it come at a cost? I remember both Olympus and Leica making a big deal about the issues with non-parallel light rays at the edges of digital sensors, and how that caused a sort of vignetting not found with film (where the emulsion is basically non-directional). It seems to me that a shorter flange back distance would force light rays outside of the center of the frame to be even more oblique. Am I misunderstanding how this works?

The Sony E-mount is almost as close. Is this shorter distance all advantage, or does it bring problems as well? (Clearly, it means all-new lenses, but it should also make adapters easy.)

Asked by mattdm

Answer

The short-flange distance gives more latitude to lens designers.

There is no disadvantage at all to a short flange distance because the lens does not have to use it! Case in point, you can adapt almost any lens to a camera with such a short flange distance.

In general, digital sensors prefer light to hit it with a more uniform angle, so lens designers probably wont feel necessary to take advantage of the shorter distance except to create something more compact.

Answered by Itai

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Can I use an old Olympus-mount lens on a Canon DSLR?

Question

What is the mount adapter I need to mount a Vivitar 28mm 1:2 No.22 (made by Kino, aka Kiron) lens on my Canon 600D? Is it the T/T2 lens mount?

I used to mount this lens on my dad's Olympus OM-10.

Asked by Akram Mellice

Answer

No. (I should clarify that. I mean, "no, that's not the right adapter." The answer to the underlying question, "can I use an Olympus OM-mount lens on my Canon EF-mount camera," is clearly, "yes.")

The T-mount lens is a screw-mount type introduced by Tamron as a universal mount (to be used with adapters to fit the various camera brands), and is a sort of precursor to their later Adaptall/Adaptall2 mount system. These days, the T-mount system is used mostly as an interface between cameras and other optical systems, like telescopes, microscopes and binoculars (using only one of the two optics, of course).

You would need an OM to EF adapter, like the Photodiox model listed here. Luckily, the OM mount had one of the longest flange-to-film distances ever, so the adapter is just a simple bit of metal with no additional optics, and will still allow infinity focus. Whether the adapted lens will work on your camera depends on whether your camera allows lenses with no electronic linkage to speak of to work (it varies by model—check your manual).

Answered by Stan Rogers

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Mount old lens on Canon Rebel T3i using Canon FD/FL Lens to Canon EOS EF Body Mount Adapter

Question

Can I use any of the following lenses:

this or this or this or this with this adapter for my Canon Rebel T3i?

Please explain if any pitfalls that I may encounter such as infinity focus.

Also suggestions for cheap old high range zoom lens (such as 70-300mm) are welcome even if they are using another adapters

Asked by Akram Mellice

Answer

FD lenses are designed to sit closer to the film/sensor than EF lenses - so there is no adapter that can just place the lens in the correct location (because the correct location is inside the camera where the mirror is).

This leaves us with to options:

1. Adapter that places the lens farther than it's supposed to be - this has the same effect as placing the lens on a macro extension tube, you lose the ability to focus to infinity and from what I heard you are likely to lose the ability to focus behind macro range.

2. Adapter with a lens to corrects the distance difference (like the adapter you linked to) - so you just take an old lens (that is not as good optically as the new ones) and run all the light trough a second cheap lens degrading image quality even more.

So, if you mount FD lens on an EOS camera you have a choice, you can have an impractical focus range or bad image quality - and as an added bonus you also lose auto focus and other niceties of your camera.

If you want to use cheap old lenses you should choose lenses for a mount that has an adapter that can place the lens at the correct distance without optical corrections, basically and mount with the distance grater than what EF uses (you can use this list) - but you still lose a few decades of advances in camera and lens technology, don't expect the old cheap lenses to be nearly as good as the new expensive lenses.

Answered by Nir

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“One size fits all lens” for Sony and Nikon, or a Nikon lens plus adapter?

Question

I've been taking photos with the supplied kit lens with my Sony Alpha 200 for the last couple of years. I'm looking at changing the body to a Nikon D7000 at some point in the future and I'm also looking at getting a 50mm prime lens.

My question is, which lens can I buy that would fit a Sony Alpha 200 and also a Nikon D7000? Should I get a Nikon lens and a lens adapter or is there some form of 'one-size-fits-all' lens?

Asked by Anish Patel

Answer

There is no such thing as a universal lens. The shape of the connection, position of the contacts (and electric protocol too), distance between the connector and sensor are all different.

There are adapters to bridge the gap which are mostly used for legacy lenses. The reason is that with those adapters you will lose most communication between the body and lens, so you have to focus manual, probably have to set aperture manually and sometimes will have to use the camera in Manual mode only (no metering).

There two extremely important points to note above: - If the lens you use (such as ALL kit lenses for DSLRs) does NOT have an aperture ring, you will only be able to shoot at one aperture (usually either the smallest or the largest). - If you adapt a lens who is supposed to sit closer to sensor, it will be be able to focus very far and you will almost certainly lose infinity focus.

Given all this and my understanding that your lens investment is minimal, I would recommend simply buying the lenses you need for your new camera.

Answered by Itai

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How do I identify unknown thread mounts?

Question

A local thrift store is selling a macro bellows with thread (screw) mounts. The mount is not identified. I have a cheap digital caliper. What are the likely mounts that it could be, and how can I distinguish them through measurements?

I know, for example, that there's a nominal 42mm "Pentax" screw mount, but what are the actual measurements that I should expect from measuring male and female mount diameters? Do I need to be concerned about thread pitch?

Answer

At 42mm, the mount could be either M42 (Pentax/Practica/Zeiss) or T-mount. The difference is thread pitch -- the M42 has a 1mm thread pitch (the "wavelength" of the thread, measured from "peak to peak"), and the T-mount has a 0.75mm thread pitch. So, three grooves in three millimeters is M42; four grooves in three millimeters is T-mount (or one of the variations on T, like the Sigma YS).

There's also a slight chance that you might run into an M39 (39mm Leica) mount, but that's vanishingly unlikely on a bellows unit. A bellows is almost useless without TTL focusing (as in an SLR ro a view camera), and the M39 is pretty much a rangefinder-only mount (the exception being the early Leica reflex box that sat between the camera and the lens).

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What are the advantages to using EF-S lenses on Canon APS-C cameras?

Question

I know EF-S lenses are "optimized" for crop sensors but what are the exact advantages to using an EF-S lens? Does it give better color, sharpness, depth of field, etc...?

In addition, do EF-S lenses still have the crop factor magnification as regular EF lenses do?

Answer

The advantages of EF-S lenses:

• Having the rear element sit closer to the film allowed Canon to use scaled down versions of existing lens designs as a starting point, cutting development costs.

• The need to project a smaller image circle allows wide angle designs to be lighter by having smaller glass elements as vignetting is not as severe.

• Having the correct size image circle helps with flare, as does having a lens hood designed for the camera sensor size. Projecting a larger than necessary image circle basically means letting extra light into the camera that doesn't contribute to the image, which is a recipe for flare as this light can bounce back off the rear element and onto the sensor.

• Projecting a smaller image circle allows sharper designs to be produced, the lenses used in compact cameras have tiny image circles but are able to resolve many more line pairs per mm than SLR lenses. So all being equal (which it never is!) an EF-S lens on APS-C camera would be slightly sharper than an EF lens on APS-C. It wouldn't be shaper (in terms of line pairs per picture height) than an EF lens on FF, but that's another question - for more information see:

With all other things equal, in a DSLR, will a larger sensor produce a sharper image?

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What is the reason to change the mount type in Nikon 1 series?

Question

To use Nikon F-mount lenses, Nikon 1 series require an adapter.

Moreover, the flash unit mount is a custom one too and it seems that there is no adapter at all, but maybe I'm wrong.

What is the technical reason to use custom mounts for this new brand, while there are obvious disadvantages of not keeping the mount which already exists for a half of a century, and the hot shoe which is largely compatible with most manufacturers?

Answer

The Nikon SLR lenses are designed such that the image circle falls on the sensor/film plane based on the distance from the sensor to the mount (flange focal distance). For an SLR, this distance includes the space needed for the mirror. As the Nikon V1 doesn't have a mirror, the distance from the sensor to the mount point is substantially smaller, so in order to use an SLR lens you need an adapter to create the distance. This adapter does just that.

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Does using a lens adapter change focal length?

Question

Does using a lens adapter change the field of view?

I recently bought a Sony NEX-5, an extra Minolta MD 50mm 1.7/f lens and a MD to E-mount adapter and I was wondering, as the adapter increases the distance between the sensor and the lens by ~10mm, does this effectively make my 50mm lens a ~60mm lens? Or am I just misunderstanding things?

Answer

It won't change the focal length of the lens, that's what a multiplier will do. You'll see these out there, often as a 1.4x or 2x multiplier with optical elements in them. These are designed to multiply the focal length of the lens.

In general, extension tubes, which is what is normally used to move a lens further away, are there to allow closer focus than a lens would normally have, thus giving them macro, or close to macro, ability. However, in doing so, they'll result in loss of infinity focus (which isn't an issue in macro photography). Nevertheless, they do not change the focal length of the lens.

In the case of your camera, however, the adapter is moving the lens further away from the sensor but it has to in order to continue to focus the same. The lens is designed to sit on an SLR and that means it's designed to focus onto a sensor (or film) that is further away from the rear element of the lens than your NEX-5.

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Are there any decent telescopes for around $250 that I can mount my Canon 60D to?

Question

I am looking to buy a telescope for about $250, are there any at that price range that can be mounted on a Canon body?

Answer

You don't tend to get telescopes designed for a particular camera, what you need to look for is a telescope camera mount for your 60D. This is a device which replaces the eye piece on the telescope with an EF mount which the camera is connected to instead of a normal lens. The adapter usually consists of two parts. A 'T' adapter which fits directly onto the telescope and a 'T' ring which provides the correct coupling to any given camera. Using an adapter such as this you will be able to connect your camera to pretty much any telescope. http://www.telescopehouse.com have a good range in their online catalog in the Astro Imaging section and, although its a UK site, it will at least give you a good idea what to look for. There are lots of low end telescopes in your price range that a camera adapter can be fitted to which will give you pretty good results.

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Is there an adapter for Canon AE-1 lenses on Canon 550D?

Question

Is there a way to use my old Canon AE-1 lenses on my new EOS-550D?

Answer

Short answer: yes, but you won't like the results.

Longer answer: those old lenses sure are fun :) ... but you still won't like the results. Here are some details:

There are adapters, and you can by cheap glassless ones (that won't allow infinity focus -- they basically act like extension tubes) or adapters with glass to allow infinity focus but that have varying quality (depending on how much you are willing to pay -- Canon even made an extremely expensive official adapter, I've heard, decades ago to help pro photographers with the switch from FD to EOS).

Unfortunately, your quality will really suffer. When I got my 30D I bought a couple FD lenses (my crown jewel was a 135/2.8, beautifully small and responsive and light-weight) but in order to use them with my adapter I had to stop them down 2-3 stops in order to get good pictures without CA. I still loved using that 135, and in the right light I could still get a decent picture every once in a while at f/2.8, but for all practical purposes it was a 135/8 and it's hard to get excited about a 135/8 and want to take it out for pictures.

With the 135 and the glassless adapter, the maximum focus distance was about 6 feet. With a 100-300 at 300mm, the maximum focus distance was, oh let's say I was 15 feet from a house and I could just barely focus on something at the top of a two-story house so what's that, 25 feet? Somewhere around here there's also a question where I both calculated and experimentally determined the maximum focus distance of a 50mm lens with a glassless adapter (it wasn't pretty).

If I were you, I certainly wouldn't throw out your lenses: I'd spend a few dollars on a glassless adapter and consider spending a few more on an adapter with glass to allow infinity focus. You can use the glassless adapter to turn your wider-aperture lenses into macro lenses (I use one with a 35-70 f/3.5-4.5, but the smallish aperture makes focusing difficult and I'd like to get an f/2 or wider lens for that purpose), and the adapter-with-glass to run some experiments. But I'm sure that you'll get better pictures with a cheap all-plastic slow consumer modern lens (especially one with modern coatings, which also play a big part in image quality) that doesn't require an adapter than with your expensive-at-the-time fast lenses with an adapter.

I'm sorry to be the bearer of bad news... and if you can prove me wrong, I'd love to hear it!

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Olympus T2 Adapter ring stuck on my Sony Alpha — how can I get it unstuck?

Question

Edited. I bought a Samyang 500mm Mirror lens off ebay so that i could try and expirement with tele photos before i decided to buy really expensive lenses..

I got the lens with a T2 Adapter (Olympus) Written on it [Edit-This ring is about 3mm to small for the Sony Alpha and the flanges are shorter- so it slips past the locking mechanism and 'gets stuck' in the void..]

which i screwed on to this side of the Lens [Edit- Cheaper than other.. but a bit of practice and get nice photos.. for the price ;) ]

[Edit - I was doomed from the start.. The auction is misleading in its words and meant you can buy an adapter but they make it sound as if one fits all- or the correct one is included- buts its not.fine print]

As usual I aligned the red dot the the Alphas red dot- put it in and screwed clockwise.. a bit unusual at first as it rotated about 1/4 around.. and my other lenses only twist and lock quickly..

I did not make anything off it and started experimenting and taking photos all looks OK.

Then when i try to unlock the lens anti-clock wise.. I realised there is play- that its not actually locked in properly... and there is about 1/2cm play either way on rotation and I cannot remove the adapter :( The actual lens screws of the apter ring but the ring stays in :( I press the release button and nothing- it wont turn any further.. I tried slight force and nothing. wiggling it up down-.. it stuck - but loose.

Can anybody advise how to remove the damn ring.. is there a a release inside the barrel somewhere? can i unscrew something to get to the mechanism.. I know the mirror need to be untouched and work in a dust free environment.

Surely i am not the only plonker that has done this.. I actually ordered the correct adpater now.. but the original sale description says this

-T2 adapter ( allowed you to used it on other brand camera) SAMYANG 500mm MC

f/8.0 Mirror Lens works with following cameras: - Canon EOS 5D, 50D, 40D, 30D, 20D, 10D, 450D, 400D, 350D, 300D, 1000D, 7D - Nikon D3X, D700, D300, D200, D100, D90, D80, D70, D70s, D60, D50, D40, D40X, D3000, D5000 - Sony Alpha A900 A850 A700 A550 A500 A380 A350 A300 A230 A230 A200 A100 - Olympus E-30, E-3, E-520, E-510, E-500, E-420, E-410, E-400, E-330, E-300 - Pentax K20D, K10D, K200D, K110D, K100D, K100D Super, K-m AND MANY MORES

Some thing similar happened to this guy- dont know what he did in the end

and even the guy selling it said it will fit straight in... I am so annoyed.. Please help

Answer

Well, in the link you posted the Pentax forum, the guy mounted the lens back on the camera for extra grip and slowly applied force and it eventually came off - so there's that option...but...

The safest option is going to be to take it to local place or send your camera in to have it removed. If you damage the mount while trying remove it yourself through force you could end up spending quite a bit of money.

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How do I find out which Nikon film cameras will work with my newer G F-mount lens?

Question

I want to pick up a film camera but I have a nice G lens (Tamron 17-50 f/2.8 with VC) and I'd really like to be able to use it.

I'm having a hard time understanding which cameras will be able to work either fully or partially. For example, if I put it on a Nikon FM3A it would work but without any aperture control or autofocus right? Most of the backwards compatibility charts I've seen are extremely confusing.

Answer

The two lens compatibility resources that I know of are nikonians.org and Ken Rockwell. A caveat is that they only deal with Nikon lenses; it's a harder question to answer with your Tamron.

If it really is like a Nikon G VR lens, then with the FM3A it won't work at all, but it won't damage your camera to attach it. On the other hand, everything including metering, focus, and VR would work on an F100.

Edit

Of course, as danio says, the lens needs to have a sufficient image circle to cover the film. This lens doesn't, so it won't work on any 35mm film camera unfortunately.

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