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Author Topic: Help to understand "long" exposures on Leaf Aptus  (Read 1323 times)
torger
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« on: March 19, 2012, 01:11:32 PM »
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A second hand Leaf Aptus 22 is still on top of my list for entry level MFDB for my tech camera.

The riskiest aspect of this back seems to be "long" exposures. The information you find on the net about these old backs is usually people that have all sorts of strange problems when these backs were new, probably caused by buggy firmware or early hardware issues which has been fixed later. I've been unable to find out what the status of long exposure of an up to date Aptus 22 back is though.

Using it outdoors at f/11 early morning and evenings there will often be multi-second exposures. If the official number of max 30 seconds is virtually indistinguishable from 1/100, I'm ok although the ISO25 makes it tight. If 1 - 2 stops of DR is lost due to thermal noise I'm not ok.

I do know that CCDs need efficient active cooling to work really well for long exposures, like astro cameras have, and MFDBs don't have that. So I don't have huge expectations, but at some point it becomes too poor for my use case. I want to make sure the Aptus 22 can reach the decency level.

There are usually two aspects of long exposure noise, background thermal noise that reduces overall DR, and hot pixels. I'm not worried about hot pixels as long as they are not too many or too clustered. Strong reduction of DR due to thermal noise is my worry. MFDBs is often praised for their high DR, but when reading about long exposures the term "software noise reduction" and discussions along the lines that "DR is not really that important after all" comes up a bit too often. I don't know if software is used just to remove hot pixels or if it is to mask thermal noise, which of course won't bring back lost DR. I know that great DR can only be had at lowest ISO, which is ok, but if it also requires sub-second shutter speeds I'm in trouble.

It's also a bit unclear about the dark frame, is it auto-made and auto-subtracted from the raw file or not?

If the Aptus 22 is poor, is Aptus 75 any better? Someone recommended to me an Aptus 75 above the 22 without saying why, not sure if it was resolution or if the 22 actually does suck at multi-second exposures and the 75 is significantly better. I know Phase One P25+ is great, and it does seem like the P25 despite limited may actually be significantly better than Aptus 22, but it is hard to find clear answers, and as usual RAW files cannot be found...
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Peter Devos
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« Reply #1 on: March 19, 2012, 01:33:53 PM »
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I think long exposure is worst on the Leaf Aptus 22. I used almost all backs between 6 and 50Mp and the worst definetely was the A22. Not only long exposures but also dark parts of an image at 100 iso. At 25 and 50 Iso, the A22 is one of the finest backs i ever used. Just do not go above 50 iso and you will have the finest images possible. I really prefer the rendering of the Kodak CCD in the Ixpress132c and CF22 backs. They are really good up to a good 20 seconds. Just my humble opinion :-)
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torger
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« Reply #2 on: March 19, 2012, 02:20:06 PM »
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Thanks for the reply. Since I'm used to 5Dmk2 it is great to hear comparison with that. The reason why I've got a medium format camera is that I want the lenses and movements of the technical camera. The 22 megapixel back is just my way to entry at a low cost, I plan to upgrade to say P45+ in a few years when prices has come down. So now I'm just aiming at "good enough" as the first step. I expect a minor upgrade in image quality from Canon 5Dmk2 at lowest ISO in the whole shutter speed range. I know it is better at short shutter speeds, but say if everything above a couple of seconds is actually worse than the 5Dmk2 I won't be happy.

However, I can probably stretch the budget to an Aptus 75 for example if Aptus 22 simply is not good enough with today's standards. Or perhaps just go for the similarly priced P25 which some seem to be able to stretch a little bit past the official 30 second limit. I know the P25+ is great, but it also costs about as much as the 33 megapixel Aptus 75 on the second hand market.
« Last Edit: March 19, 2012, 02:23:36 PM by torger » Logged
yaya
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« Reply #3 on: March 19, 2012, 02:46:42 PM »
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32 seconds, f11 @ 25 iso (RAW file)

There are a handful of hot pixels in the deep shadows that can be taken out easily with either the Single Pixel slider in Capture One or the "Clean Long Exposures" option in Leaf Capture

Other than that I think this is a good example of what the Aptus 22 can do in certain conditions. Low ambient temperature can always help!

Regarding the dark frame; it is taken automatically (and then calculated) whenever the exposure goes beyond 1/15 or if you change the exposure time (for example if you work in P mode)

If you do consecutive long exposures and see noise building up you can change back to a short one (e.g. 1/125) to force the back to reset itself and then carry on.

The Aptus 75, being a stop faster, will give you shutter speeds twice as long for the same exposure and since the files are bigger the noise will be less visible at the same print size

Yair
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Yair Shahar | Product Manager | Mamiya Leaf |
e: ysh@leaf-photography.com | m: +44(0)77 8992 8199 | www.mamiyaleaf.com | yaya's blog
torger
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« Reply #4 on: March 19, 2012, 03:06:32 PM »
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Thank you very much Yair, raw file was really helpful. From that it does look like it will meet my expectations. I see only some hot pixels, but not any bad overall noise. Nearly always when it is a bit darker it will be a bit colder weather too here in Sweden, typical around 15 degree celcius.

I just shall go through some old files and see what kind of exposure times I need... ISO25 / 32 seconds corresponds to ISO100 / 8 seconds on my 5Dmk2, so I will indeed hit the limit at times, just don't know how often yet.
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torger
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« Reply #5 on: March 20, 2012, 02:29:10 AM »
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I've looked through my work from the latest year, and while I did not think I did much long exposures, there's quite some 10 - 20 second exposures there at f/8 ISO100, that means 80 - 160 seconds f/11 ISO25. I thus may need to rethink (= expand my budget :-) ).
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Fritzer
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« Reply #6 on: March 20, 2012, 01:34:06 PM »
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I don't really have much experience with other backs, let alone the A22, but I'm still using the Aptus 75, mostly in the 2-12s range, sometimes longer, 50-100 ISO, 'Clean long exposure' checked in Leaf Capture (lots of hot pixels otherwise) .

I have hardly ever seen any recognizable shadow noise, and it is certainly in a different league from my Canon 5DII, in particular for long exposures .

However, I'm shooting still life, low volume and little chance for the back to overheat .
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Audii-Dudii
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« Reply #7 on: March 20, 2012, 02:02:22 PM »
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If you do consecutive long exposures and see noise building up you can change back to a short one (e.g. 1/125) to force the back to reset itself and then carry on.

If you don't mind, please explain what you mean by "force the back to reset itself" by making a short exposure after a long one.  What does this accomplish and how does it affect the performance of the back?

Thanks!
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