What attributes should I look for when buying batteries for a flash?

Question

I want to buy some more rechargable batteries (AAs) for my flashes.

I suppose I mainly care about: - Quick recycling of the flash - Hold their charge when not in use

Although bonuses for: - Long lasting (on a single charge) - Long lasting (before they need to be thrown away (recycled) )

Is brand important? What types are available? Show I just get the highest mAh?

Answer

1. Use high-quality NiMH cells

• You want the NiMH chemistry because it's able to supply the high peak current that leads to faster recycle times (and less energy lost to internal resistance).
• "Hold their charge when not in use" and "long lasting (on a single charge)" are opposing criteria: the reason is that the newer low-self-discharge (or "hybrid") cells have a lower capacity than standard NiMH cells (for example, the last time I was buying, you could get 2600 mAh in regular but only 2100 mAh in low-self-discharge). A rule of thumb: if the batteries are going to sit for more than a month in a ready-to-use state, get the low-self-discharge variety.
• Yes, a good brand is important, though the NiMH market is not dominated by Energizer and Duracell as the alkaline market is. Don't just buy the highest mAh - you'll get scammed. Good brands include:
  • Sanyo
  • Powerex (Maha)
  • Energizer
• Dave Etchells has written up some great capacity tests (though they are somewhat dated now).

2. Use a high-quality charger

• This is very important for cell life and capacity. It turns out that you need rather fancy circuitry and algorithms to charge NiMH cells (a) to full capacity and (b) in a way that is not damaging to them. Do not go to Target and buy whatever charger they have.
• Important qualities include:
  • Individual charging circuit for each cell.
  • Testing and refresh cycles.
  • Appropriate sensing and algorithms for charging.
• I personally use and recommend the LaCrosse BC-900, which doesn't seem to be available any more (it seems to have been replaced with the BC-9009).
• Another good brand is Maha, which has several chargers which meet the above criteria (the MH-C800 series and the MH-C9000, perhaps others).

3. Manage your battery collection

When you put four cells into the flash, the capacity of the group is limited by the weakest cell. Managing your collection minimizes this inequality. Key things to do include:

• Number your cells so you can keep track of each one. I use a Sharpie, but this wears off so I have to re-label from time to time (I label each cell twice to reduce the chance of losing the number to wear).
• Keep the cells in sets (i.e., don't just keep a pile of batteries and choose four when you need them). This exposes the members of each set to the same wear and environment, so they stay equal.
• Regularly test your cells. This will let you identify and deal with cells that are going bad (they will have diminished mAh capacity). I wrote a Python script (battman) for this purpose, but a spreadsheet will work just as well.
• Bad cells can often be repaired using the refresh cycle on your charger.
• Note that new cells sometimes have a capacity significantly lower (say 10-15%) than their rating. That's just how it is and doesn't indicate a defect. The better brands won't do this.

More info

• http://batteryuniversity.com is a great resource for learning lots more about batteries.
• http://www.thomasdistributing.com/ is my favorite retailer. Their website is a somewhat bizarre, but they have a wide selection and have provided me with excellent service. All they do is rechargeable batteries, so they actually know their products. (No affiliation, just a satisfied customer.)

(Suggestions welcome in comments - I'll edit.)

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How are watermarks typically used in images?

Question

How many watermarks(number) are used on an image commonly? What type of watermarks are used?

Answer

A single watermark is most common, and mainly serves as a notice that the image is copyrighted. A single watermark is often easily removed with editing, like photoshop's content-aware fill. They tend to be a semi-opaque grey in order to not ruin the picture entirely, while being visible enough to serve their purpose.

An important point is that an image is copyrighted at the moment it is taken, and this is unaffected by the presence or absence of a watermark. So adding a watermark does not increase your legal protection.

They can also be used as a branding tool to advertise a photography business, as opposed to trying to discourage misuse of the image. A name and website so anyone who likes an image they see online can search and find the photographer.

Some agencies, like this one for example, cover their images with their watermark making it very difficult to remove.

Apart from visual watermarks, there is also digital watermarking, which is quite a different thing. This is not visible to the eye, but is embedded in the image (the best analogy I know if is to compare it to digital noise in an image). A lot of information can be encoded into the digital watermark. For example, if you licensed an image to several clients, you could embed unique IDs in each copy so that if they were used elsewhere, you would know which of the images it was.

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Do very short shutter speeds result in diffraction?

Question

I'm curious if very short exposure times (say 1/8000 or even 1/16000) would cause noticeable blur due to diffraction.

To achieve very fast shutter speeds focal-plane shutters start to close the second curtain before the first one has passed completely over the sensor.

(Illustration from wikipedia)

Is the slit between the front and the rear curtain small enough to make a noticeable impact on the image due to diffraction?

Answer

Slits don't diffract; edges do. There will always be some small amount of the image exposure that arises as the result of diffraction, whether that be from a focal plane shutter or from a leaf shutter. The questions, then, are: how much of a contribution to the overall exposure does diffracted light make; and is there enough angular displacement for that diffraction to matter?

On an APS-C format camera with a 16mm x 24mm sensor and a vertically-travelling focal plane shutter whose curtains traverse the sensor in 1/250s (yielding an expected x-sync speed of 1/200s, allowing for flash duration), when the shutter speed is set to 1/8000s, the minimum gap between curtains will be 0.5mm, which is relatively enormous compared to the wavelengths of the light passing between the curtains. There will be some diffraction, of course, but the degree of interference over most of the slit width will be negligible. The "clear" exposure, the area over which the effects of reinforcement and cancellation have an insignificant effect on the overall magnitude of the incident light, will significantly outweigh the diffraction fringes around the edges of the curtains.

Focal plane shutters, too, are called that because they are very near the focal plane. There isn't a whole lot of room between the shutter curtains and the sensor (or film). The areas of the diffracted light that have significant reinforcement will not be displaced laterally very far, given that they don't have a lot of room to spread out and get comfortable. The distance between sensels on the sensor is much smaller than the width of the shutter slit, being around 7 microns these days, but that is still large relative to the wavelength of light -- light would need to spread out quite a bit before the first few bands of reinforced light (the ones having enough amplitude to affect the overall exposure) started to impinge significantly on neighboring sensels.

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What type of filters should I get for high sunny conditions?

Question

I'm planning a trip in Sri Lanka and Maldives Islands next month. In such sunny conditions, I would like to buy filters for a Pentax K20-D, to be able to take pictures of the sea, the beach, etc. (but not underwater) in the best possible way.

What type of filters are the most suitable in this situation? Do you know specific model/brand/recommendation for Pentax DSLR?

Answer

If you have trouble with to much sun, a ND (Neutral Density) might be want you want. This gives you the option of having a higher aperture even when there is much sun.

A polarization filter might also be handy. This way you could get rid of the reflections from the ocean. Also you could get that postcard feeling with a more blue sky.

There are many people who put on a UV-filter for protection. But this is a widely debated issue. I will not go into detail about that, but here is an article on the subject. Bear in mind that a UV filter might introduce a lens flare, especially when there is much light.

You can stack several filters, like the ND and the polarization filter. However there might be problems with vignetting. This also depends upon the lens you are using.

Personally I use Hoya filters because I consider they to be of high quality. However I have no scientific evidence that they are better than other brands.

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Alternative to 4/3 camera without compromising quality

Question

I have a Panasonic DMC L1 (the first 4/3 camera) with Leica zoom lens and an Olympus fixed focal length lens. The Leica lens has developed a problem and the insurance cant repair it. They are going to offer me an alternative ..likely to be a camera within £700. I suspect they will offer me the Lumix G series. I quite liked the micro 4/3 cameras as they are smaller. However, I suspect the picture quality, esp night time without the excellent bounce flash on L1 would be not as good. I also liked the controls on the L1.

Should I go for a micro 4/3 or should I go for the 4/3 like G series?

Answer

The image quality of a 4/3 and Micro Four-Thirds camera is exactly the same since the sensors are the same size. Therefore you can expect better image quality from newer 3/4 or Micro 4/3 cameras due to technological improvements.

It is normal that there will be differences when changing models and even though what you are getting will be some kind of upgrade, there will be some things you will like less.

One improvement over previous generations is that newer cameras focus much faster. So, at this point, without knowing much about your photography style, all I can say is that you choose the right model considering your needs. If you like using direct controls than you should look at advanced models and if you are more comfortable using the camera at eye-level, so you should look at the models with a built EVF. Finally you can always get a 4/3 DSLR from like the Olympus E-5.

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Do differences in color saturation across Nikon and Canon pictures matter?

Question

I am about to buy a new DSLR and shortlisted the two models, Nikon D5100 and Canon 550D.

From the pics that I have seen on Flickr it seems that Nikon pics have more saturated color than Canon. Is it true? Also will it be possible to take similar pics from Canon 550D ?

I heard from a Canon 550D user that you can get similar results from a 550D too. On the contrary I heard from some enthusiasts that you need to do a lot of post-processing on Canon pics if you want to achieve Nikon like results because a Nikon sensor by default puts in more color. He went on to add that Canon pics are closer to real world colors while Nikon gives more saturated colors for eg. the sky would look more blue with a Nikon.

Answer

The only fair way to compare something like saturation is a RAW-to-RAW comparison under conditions and settings that are as faithfully-duplicated as possible. As others have mentioned, saturation is one of the things that's typically affected during image processing -- even the processing done in-camera when a JPG file is created (thus, most users don't even realize it's happening).

You might find that the only way you'll get a really good answer is to set up a test on your own, but you might find a good starting point would be to review files produced by a review site like DPReview. They have test reports for both the D5100 and the 550D, and both of these reports have a section showing RAW outputs of their standard test scene.

The test for the D5100, in fact, will let you compare RAW outputs of the D5100 and 550D interactively at various ISO settings. On this screen, you can not only compare the outputs, but you can also download the RAW files produced for the test. These RAW files might be the easiest approximation you can find for purposes of an apples-to-apples test.

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What lenses will work best for desert landscapes?

Question

I'm going to be travelling to the Middle East soon and was wondering what the best setup for photographing desert landscapes would be. Here's what I have:

Canon 7D

EF 50mm f/1.8 II

EF-S 18-135mm f/3.5-5.6 IS

It turns out the above lenses are not weather-sealed. I can probably go to a lens rental service. In this case, what are some good Canon (or any EF-mount) lenses that are weather-sealed and good for desert photography?

UV Filter

Tripod

Also, does anyone have any general guidelines/tips for photographing in the desert?

Answer

Those lenses will die in seconds in the desert if there is wind. Actually I saw another non-weathesealed Canon lens stop working in less than 10s while in the Peru desert. In Egypt we had more luck but still a lot of people in the group had sand infiltrate their lenses. This is a good time to use a Clear or UV filter too as even a weather-sealed lenses get scratched, the filter will be ruined after that. I had an expensive polarizer damaged on the first sand-dune, luckily nothing happened to the weather-sealed lens I had.

Fortunately you have a weather-sealed camera and you shout match it with weather-sealed lenses. There are plenty for Canon mount. Normally for landscapes people go with something on the wide side but a medium telephoto is good to compress perspective which renders desert photos more interesting. The 17-40mm F/4 or 24-105mm would both make great choices. On the 7D the 24-105mm does not give you wide-angle, so you probably want a wider lens for monuments and such.

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