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04-13-2013, 01:21 AM   #1
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645D and Depth of Field

Hi all,

This is my first post here as I am considering a 645D system and have a few questions.

When comparing to 35mm Full Frame, how much further do you have to stop down the lenses to get a similar deep depth of field on the 645D as I would at say F8 on 35mm FF? Meaning, to get the same DOF for the same field of view, if the 35mm is at f/8, would the 645D have to be at f/11, or f/13, or f/16?

Can the 645 lenses handle being stopped down more without suffering from diffraction softening the images? I know on my Leica M9, anything beyond say f/8 with a 21mm Super Elmar will start to reduce contrast and overall sharpness.

Also, of those who are using the 645D, how do you find the LCD for checking critical sharpness across the image? Is it accurate enough?

Finally, I shoot many seascapes and waterfalls etc and using ND filters can often put my exposure longer than 60 seconds. It is this reason alone that I am considering not getting the new Leica M as it is restricted to 60 seconds max exposure at base ISO. How is the 645D at exposure times longer than 30 seconds, say at 60, 90 and 120 seconds? Are the files still clean and free of banding etc?

Any help would be greatly appreciated. My new Leica M is on backorder and I have about 2 weeks to decide to ditch the M system, keep my NEX and go with a MF or SLR system.

Thanks, Scott

04-13-2013, 02:55 AM   #2
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I am itching to move to Leica MM, and I have been thinking about parting with my 645d and related lenses. My other cams are M8, K0-1, and Q.

Exposure beyond 30 secs at ISO of 100 isn't all that impressive to me. Banding is rather annoying, although my experience with other digital medium format systems is zero, so comparatively speaking I am not so sure how good or bad.. Exposures nearing 60 secs I have played with but not with satisfactory results. Perhaps other operator of 645d here may have had better luck, and if so love to learn few pointers.

LCD screen is small for MF, I think. Functionally speaking, it is easy enough to zoom in and maneuver around and about within the frame. Tethering is possible with a $200 software purchased from Pentax. I don't own one, and how helpful this may be for your purpose I am not sure. I for one would like one but it is a bit goofy paying $200 when the camera + kit lens costing $10,000. I mean I understand tht if you can afford this what is another couple of hundred bucks, but it is to me nuisance nonetheless. But, VF is quite nice, as it was in 645n.

As far as lenses handling stopping down, I hear that there are good performers, then lame ones. Interestingly, I tend to prefer results obtained with 67 lenses than 645. I am not sure why. Perhaps it is a matter of preference. I have a 67 165 mm that I can stop down as I wish. A 120 macro is pretty good as well in this regard. The kit lens DFA 55 seems the sharpest at about f/11, but in all honestly you probably would not notice deterioration in sharpness for at least two more stops. A35 past f/11 isn't all that great, but I heard that FA 35 645 is much better. The sleeper lens to me is FA 75 645. For less than $300 typically, it really performs well, and in some situation it doesn't feel "too long" for landscaping shots. Pentax has DFA 25 mm 645 and I am actually very impressed with the files I have seen.

All in all I think 645d is an interesting camera. Certainly not what I expected digital medium format to be, but mostly in good ways than otherwise.
04-13-2013, 05:11 AM   #3
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Scott:

My impression after 2.5 years with 645D is that, in general, diffraction effects start to cause softening at f16. The screen is useful, but utimately you need to check the raw file on a larger screen. I don't do many long exposures, but the few I have are fine. Unlike Fontan, I see no banding. Here's an 100% crop from a five minute exposure of star trails (and a plane) in a sky with considerable light from a nearby city.

here
04-13-2013, 05:25 AM   #4
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That's a good question but I am unable to answer it. However, I have been wondering about something like that as well. When one wants to shoot a landscape with a large DOF, what are the equivalent apertures using for example a small sensor P&S camera, an APS-C DSLR, medium format or large format film? The bigger the sensor or film is, the narrower the DOF is at the same aperture. So to increase the DOF, one must stop down more. Provided we're shooting still landscapes at low ISO and a good tripod (making the exposure time a non-issue), what is the prefered format? Does the diffraction begin to limit the IQ?

04-13-2013, 05:35 AM   #5
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Well 645D with FA150mm/f2.8 set at f4:



When comparing images, you need to create the same FOV and then the DOF off the 645D is much thinner then on smaller platforms like aps-c. So going to f8 or more still gives you a good isolation on a medium telelens.
04-13-2013, 08:43 AM   #6
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You can stack multiple 30 second images ( or whatever time you prefer) to create equivalent longer exposures. Do a search for examples on the technique. Exposure blending and focus stacking are also common techniques employed. Modern landscape photography seems to have become more like data collection than old-school photography.
04-13-2013, 11:45 AM - 1 Like   #7
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Regarding DOF between the two system, there is not much difference between a system with a sensor diagonal of 44mm (35mm sensor) and one with a diagonal of 55mm (645 sensor). A normal lens on each would be 44mm and 55mm respectively. For the 55mm to have similar DOF as the 44mm, the 55 would need to be stopped down 1 stop more. That is not a show stopper. Diffraction is something we have to live with at times to get the DOF we need.
04-13-2013, 12:38 PM   #8
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IMHO from using the 645D a few weeks and having been using full frame DSLRS in general I have to stop down 1 stop to get similar depth of field given equals.

04-13-2013, 09:45 PM   #9
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For my personal taste in sharpness for landscape images, I've never hesitated to shoot up to f/16 with any of my lenses for the 645D. After that, some lenses do better than others. I've found the 645 35mm lens pretty sharp all the way up to f/22 (it's min aperture). On the 645 D FA 25mm anything beyond f/16 starts to show a little more diffraction that I'd like...though that may be in part because it's sharper than the 645 35mm A up to f/16.

I rarely shoot wider than f/8 for landscapes, the sharpest apertures for most Pentax 645 lenses seems to be f/8-f/11.

I find the viewfinder very useful for checking focus, but not quite as useful for checking diffraction. I can tell that an image shot at f/16 is a tad sharper than f/22 using the viewfinder, but it's sort of hard to tell (but I just know it's going to be sharper, so will shoot at the best DOF/diffraction compromise). The viewfinder is nice and large IMO.
04-14-2013, 02:00 AM   #10
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QuoteOriginally posted by tuco Quote
Modern landscape photography seems to have become more like data collection than old-school photography.

tuco, could you elaborate on that please?

I don't comdemn, nor condone. I'm just curious.
04-14-2013, 03:38 AM   #11
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QuoteOriginally posted by desertscape Quote
Regarding DOF between the two system, there is not much difference between a system with a sensor diagonal of 44mm (35mm sensor) and one with a diagonal of 55mm (645 sensor). A normal lens on each would be 44mm and 55mm respectively. For the 55mm to have similar DOF as the 44mm, the 55 would need to be stopped down 1 stop more. That is not a show stopper. Diffraction is something we have to live with at times to get the DOF we need.
Thats what i had in mind.
So basically + 2 stops compared with APS-C sensor from the same shooting lens' angle
04-14-2013, 07:22 AM   #12
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QuoteOriginally posted by Adam G Quote
tuco, could you elaborate on that please?

I don't comdemn, nor condone. I'm just curious.
That's the feeling I get when I to go out with my digital camera and exposure braket a bunch of shots and shoot for focus stacking so you don't have to stop down so much. Go home, load the images up and start processing the data to make one picture. I feel like all I did was collect data. No metering to figure out because the camera did it all for you and the bracketing washes out any minor errors.

It's in stark contrast for me when I go out with my BW film where I pre-visualize the scene, meter it with my one-degree spot meter, decide what is going to be the middle gray exposure and if I need to compress the highlights during development to handle the DR of the scene. I go home and develop the film and find out if it all worked as planned. And it gives me much more personal satisfaction and reword when it does.
04-25-2013, 10:32 PM   #13
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Scott,

I moved from a Pentax 645NII to a full-frame 35mm camera, the Nikon D800E, and it was a wash in depth of field (actually, I lost a little from the switch), in particular as it pertains to hyperfocal distance. That's because film behaves differently than pixels.

I discovered this when using a hyperfocal distance chart that I've been using SUCCESSFULLY for years, based on a standard equation. I photographing a prairie landscape and the closest flower was 18 inches away. To get everything sharp, the chart said f/10 would do it. But, after taking the shot, the closest flowers was completely soft. "Huh? This should be right," I thought. After trying every f-stop and looking at the image at 100%, it only became acceptably sharp at f/18. Then, I ran some tests under controlled conditions and the results matched. The loss was a factor of 1.76 (if a stop is 1.4, then about 1-1/2 stops). According to conventional wisdom, I was supposed to gain by a factor of 1.6 when moving from MF to 35mm FF, but I actually lost 10%. This took me by surprise.

In the past, you may have used a formula like this to calculate the Circle of Confusion: CoC = Film Diagonal / 1730. Nowadays, it's ALSO a function of the distance between pixels (pixel pitch). My tests show that UNDER REAL WORLD CONDITIONS at very small f-stops (like f/22, when diffraction is an issue, but you shouldn't let it bother you): CoC = 3 x Pixel Pitch. Some say it should be 2 x Pixel Pitch. In any case, it's completely different than the film numbers and, most importantly, real world results. If you go by the old film equations, it'll be blurry. My findings show that moving to the 645D from 645 film, you're going to lose about 2-1/3 stops in depth of field. The image diagonal (sensor or film) is a factor, but the pixel pitch is now a variable that must be considered.

My findings also show that a 12-megapixel full-frame or DX sized sensor gives the exact same CoC as the digital calculation. This is why I didn't notice it in the past with my Nikon D300 (and a D700). The results were hidden because they coincidentally equaled that of film.

Now, all of this only matters if we assume, as we should, that you intend to use all 39 megapixels, like maknig really big prints. Otherwise, why waste 8K on a camera that's due for an upgrade and is about ten lenses short.

Good luck with your decision!
Mike
04-26-2013, 09:57 AM   #14
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QuoteOriginally posted by chicagonature Quote
.......................Now, all of this only matters if we assume, as we should, that you intend to use all 39 megapixels, like maknig really big prints. Otherwise, why waste 8K on a camera that's due for an upgrade and is about ten lenses short.

Good luck with your decision!
Mike
You might also mention its butt-ugly as you appear to be trying to convince yourself that you made a good choice to avoid the 645D.
04-26-2013, 11:34 AM   #15
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QuoteOriginally posted by chicagonature Quote
After trying every f-stop and looking at the image at 100%, it only became acceptably sharp at f/18. Then, I ran some tests under controlled conditions and the results matched. The loss was a factor of 1.76 (if a stop is 1.4, then about 1-1/2 stops). According to conventional wisdom, I was supposed to gain by a factor of 1.6 when moving from MF to 35mm FF, but I actually lost 10%. This took me by surprise.

In the past, you may have used a formula like this to calculate the Circle of Confusion: CoC = Film Diagonal / 1730. Nowadays, it's ALSO a function of the distance between pixels (pixel pitch). My tests show that UNDER REAL WORLD CONDITIONS at very small f-stops (like f/22, when diffraction is an issue, but you shouldn't let it bother you): CoC = 3 x Pixel Pitch. Some say it should be 2 x Pixel Pitch. In any case, it's completely different than the film numbers and, most importantly, real world results. If you go by the old film equations, it'll be blurry. My findings show that moving to the 645D from 645 film, you're going to lose about 2-1/3 stops in depth of field. The image diagonal (sensor or film) is a factor, but the pixel pitch is now a variable that must be considered.
The equation is still good, it's just that your criteria for evaluating the image has changed. Viewing an image at 100% is much higher standard (about 10 pixels per CoC if I recall correctly from the last time I did the equation) than a human's ability to resolve lines in a 'real' image.
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