richard_hopkins

I must pay more attention. I'll have a dig around. Cheers.

Richard.

Depth of field is dependent on two factors.

One is the f/number, the other is the image size. Smaller sensors inherently give more depth of field (eg camera phone) than a full-frame SLR, for example.

The difference between depth of field on a 1.5 or 1.6x D-SLR over a full frame 35mm camera is about 1.25 stops.

Richard,

"Lester Wareham , feb 20, 2007; 07:49 a.m.

I have two IS lenses, the 300 f4 IS and the 24-105 f4 IS. I turn the 300mm off on tripod because this older IS unit is known to be unstable in that condition. The more modern zoom IS unit should detect it is 'on tripod', I found it seems to be fine for tripod use.

An additional note that with the 300mm I found Mode 2 IS was about a stop better than Mode 1 IS on a monopod but handheld it did not make much difference.

I have some tests of IS performance here. http://www.zen20934.zen.co.uk/photography/LensTests/IS_Tests/index.htm"

Hello Lester,

From tests I did some years ago, I found that mirror slap was a significant cause of blurring at shutter speeds from about 1/8sec to 1/30sec. This makes logical sense to me.

But modern IS or VR should be able to eliminate this. I wonder if you have thought about repeating your IS tests at these slower speeds?

Best Regards,

Richard.

From tests I did many years ago, mirror slap is only a problem at slowish speeds between 1/8sec and 1/30sec. This is regardless of lens focal length or a number of other factors, particularly how steady your hands are, or how steady your stance is.

At shorter speeds, mirror slap is obviously reduced, usually to an insignificant level.

At longer speeds, the brief period of mirror slap vibration becomes a less significant proportion of the overall exposure, and is thus masked.

With modern lenses with IS and VR, this feature should eliminate mirror slap at all speeds.

Richard.

When a lens aperure closes down, it may not close down to exactly, say, f/8. It could be f/8.3, next time f/8.5.

Ditto shutter speeds - they are also not absolutely accurate and prone to slight variation.

This used to be a big problem 30 years ago, but much less so now.

Richard.

You must check out the Lowepro Slingshot range. They now make three difference sizes. See their website.

Richard.

Good thread. The truth is that testing lenses has always been a very complicated business, both for the tester and the user. With digital, it's even harder.

Eg contrast is usually far more important than resolution, but is much harder to measure without a 'real' MTF test bench (MTF has become an abused 'marketing' term on some websites these days). Very few of these machines exist outside lens manufactures' development departments and those that are available for hire are very expensive. They are huge, many meteres long, and need to sit on tons of heavy concrete.

I reckon you need at least 142 test traces to get a reasonable idea of lens sharpness and ideally you should test several samples of each lens, running into hundreds of traces and days of work. That's before any anlayis takes place, and there are also many other important aspects to lens performance than sharpness alone (which is mostly all that MTF can reliable measure).

Then you have the digital factor. All digital sensors are different so even if you could fit a 'better' Nikon lens on a Canon, you may not get the result you were expecting. In the film days, we could all use the same film for lens testing and the camera 'system' was not such a significant factor.

All of which leads to the conclusion that unless users are prepared to pay for thorough and conclusive lens tests, then they will never appear on the 'free' internet.

Richard.

I have used a 580EX to trigger the slave on studio lights. It's easy, after a few experiments.

First thing is to buy a box of chocolates with colour cellophane wrappers. Choose a dark red one, pull out the flash diffuser and clip it underneath. Select the loweest manual power output that will trigger the studio light.

Richard.

All lenses flare. Uusually you don't notive it, but it's there. I always use a hood, and never use a filter (except polariser) for this reason. Hoods are also very good for protection.

You have obviously invested a lot of money on your kit, so it's worth getting the right bag so you can make best use of it all. Not a lot of money overall.

I recently did the same thing as I wanted to carry a flash, and now use a Lowepro Slingshot which I highly recommend. They now make it in three different sizes.

Richard.