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11-05-2011, 12:25 PM   #1
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Using M type lenses with the K-r?

I have a large train layout and I need the depth of field that the f 22 and f32 apertures of the M lenses provide (used on my K-1000). I think the M lenses will mechanically mount OK on the Kr (I haven't ordered it yet). But will they work. I read somewhere that it requires the Av mode wide open, but another article said: "If older lenses without an "A" setting on the aperture ring are used in Av (Aperture Priority) Mode, an exposure error may occur." I would appreciate any comments, please.

11-05-2011, 12:36 PM   #2
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Yes, they are usable (however, they will NOT give you more DOF than the kit lens, they will, however, give you less (i.e. produce blurred backgrounds) if they have faster apertures)

https://www.pentaxforums.com/forums/pentax-lens-articles/110657-how-use-meter...ml#post1140019

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11-05-2011, 01:24 PM   #3
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Any Pentax-compatible lens ever made will work on your Kr. (Caveats: Some Ricoh and Vivitar lenses may need very slight modification.) Screwmount lenses need an adapter; PK bayonet lenses don't. A-type and AF lenses have aperture automation. K- and M-type and screwmount lenses require that you work the aperture manually; set Using Aperture Ring to PERMITTED in the [Custom] menu. For stop-down metering and exposure with K- and M-type lenses, use M(anual) mode and the Green button. See Adam's link above for the how-to.

Depending on how much your images will be enlarged and how closely they will be inspected, you might not want to use tiny f-stops on your Kr. The diffraction limit for an APS-C sensor is about f/9. You can shoot handheld up to maybe f/22 without noticing diffraction. You could go to f/44 for small images like thumbnails. If you use a tripod for maximum clarity, and display images large for close inspection, f/11 is about the bleeding edge.
11-05-2011, 03:04 PM   #4
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Adam, thanks for your quick reply. That's not good news. I have a K1000 and 28mm and 50mm M type lenses. I thought I'd get better DOF if I bought a Pentax K-r and used those lenses because my Canon S3IS is OK in general use, but does an absolutely lousy job when taking pictures of my train layout. I know there are situations where blurring is desired, but I'm looking for the exact opposite. Would a K-r with a kit lens do a better job for me than the Cannon?

11-05-2011, 04:09 PM   #5
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If I may jump in again: this is a DOF (depth-of-field) issue. You can plug in some numbers here and see what happens to DOF with various frames, apertures, and distances: Online Depth of Field Calculator . Note: 'frame' means the size of the film or sensor used. This makes a big difference.

For thicker DOF, use a SMALLER frame and/or a TIGHTER aperture and/or a SHORTER focal length and/or a FURTHER lens-to-subject distance

For thinner DOF, use a LARGER frame and/or a WIDER aperture and/or a LONGER focal length and/or a CLOSER lens-to-subject distance

You want thicker DOF, so your entire layout is in-focus. An advanced point-and-shoot with a small frame/sensor, short lens, and the ability to manually control the aperture, will give very thick DOF. An APS-C dSLR has a smaller frame than your 135/FF K1000; the same lens will seem to have thicker DOF on the Kr than on the K1000. Depending on your shooting distance, your M28 at f/11 might have enough DOF; if it worked well on your K1000, it'll be better on the Kr. The DA18-55 kit lens on a Kr would give even thicker DOF, say if you used it at 20mm and f/11, on a tripod. Again, plug numbers into the calculator linked above to see what happens.

You can also thicken the apparent DOF with good lighting. The P&S with slave flashes on cheap optical triggers (like about US$5 each) positioned correctly might make your train layout seem sharper. But the Kr+kit.lens and such slave flashes would give you more control over the results. Hope this helps!
11-05-2011, 04:52 PM   #6
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RioRico, thanks for jumping in. First, I have the same DoF calculator bookmarked and I understand how that works. But I think I'm beginning to see my problem- I don't understand digital cameras. The lenses on digital cameras don't show an f-stop versus DoF scale. I know my S3IS only goes up to f8, but I think that's not quite the same as f8 for a film camera. Now, the spec for the 18-55mm kit lens for the K-r lists a Maximum aperture of F3.5-5.6 and a Minimum aperture of F22-38. I don't know why there are two numbers, but f22 or 38 should give me a much better DoF than I can get with the Cannon.
I should mention that I can throw a lot of light on the layout, use a tripod, and for hands-off-operation (if there is no provision for a remote shutter release) I can use the timer.

The bottom line is that if I'm going to spend $600+, I want to be sure that I'll see a considerable improvement over the Cannon S3IS.

Your comments would be greatly appreciated.
11-05-2011, 06:22 PM   #7
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QuoteOriginally posted by Opahujo Quote
RioRico, thanks for jumping in. First, I have the same DoF calculator bookmarked and I understand how that works. But I think I'm beginning to see my problem- I don't understand digital cameras. The lenses on digital cameras don't show an f-stop versus DoF scale. I know my S3IS only goes up to f8, but I think that's not quite the same as f8 for a film camera.
F-stops have the same meaning on all lenses. It's a fraction, the ratio of the aperture diameter to the focal length. So if a 100mm lens has a 25mm aperture, the ratio is 25/100 or 1:4, and the f-stop is f/4. What's important is that the P&S has a MUCH smaller frame (sensor) than a Kr or K1000, and thus uses MUCH shorter lenses, which have MUCH thicker DOF. That's why I use a tripodded P&S (on timer) to shoot small objects, because its actual 10mm lens at f/8 has essentially infinite DOF. I don't know why your Canon wouldn't give clear pictures unless it's not focusing right.

QuoteQuote:
Now, the spec for the 18-55mm kit lens for the K-r lists a Maximum aperture of F3.5-5.6 and a Minimum aperture of F22-38. I don't know why there are two numbers, but f22 or 38 should give me a much better DoF than I can get with the Cannon.
You get two aperture numbers because they describe the extreme focal lengths. At 18mm, the f-stop range is f/3.5-22 and at 55mm the range is f/5.6-38. And you don't need (or want!) f/38 for shooting your track. I shoot a lot on my K20D with a 21mm lens at f/16. If I focus to 4ft / 1.2m, the DOF is 2ft / 60cm to infinity. (I'm reading off the lens scale, adjusted for format-faktor.) The Kr kit lens will behave exactly the same way. And yeah, it's a shame digital lenses don't have inscribed DOF scales. That's why some folks use iPhone apps, eh?

You *should* be getting sharp pictures with your Canon. Check its focusing. Good luck!

Last edited by RioRico; 11-05-2011 at 07:42 PM.
11-06-2011, 09:40 AM   #8
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QuoteQuote:
What's important is that the P&S has a MUCH smaller frame (sensor) than a Kr or K1000, and thus uses MUCH shorter lenses, which have MUCH thicker DOF
Please correct me if I'm wrong, but the way I understand it now, is that f8 on a P&S is the equivalent of a much higher f number on, say, the 35mm negative of a film camera.

I hope you'll bear with me, because I'm sure that I'll have more questions as I think about this. I turned 80 last May and I have been taking pictures and even developing my own B&W film since back in the early 1950s. But then there was a long hiatus for a carrier and raising a family. After that I bought a Pentax P30T, 35-80mm and 50mmm lenses, an extension tube set for close-ups, hot shoe multi-flash adapter, and more. Sold it all on e-bay for $80.99 net because I'd go all digital. :-(( I'm still kicking my butt about that.

Back on topic: Regarding the 18-55mm kit lense. I don't recall ever using the optical zoom on the Canon - I just don't need it. I either get closer or crop and enlarge on the PC. So, for the K-r I'm thinking about 50mm lens, either the M type I have or buying an A type. I'd appreciate your thoughts

11-06-2011, 10:42 AM   #9
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QuoteOriginally posted by Opahujo Quote
Please correct me if I'm wrong, but the way I understand it now, is that f8 on a P&S is the equivalent of a much higher f number on, say, the 35mm negative of a film camera.
The f-stop number system is designed specifically so *exposures* are standardized across platforms and lenses, so that frame and glass and iris dimensions needn't be considered when metering and exposing. If we have 110, APS-C, 135/FF, 645, and 6x9cm cameras with 20mm, 40mm, 60mm, 80mm, and 100mm lenses respectively, all shooting the same subject at ISO 100 and 1/100 sec and f/8, the *exposures* are all the same. The FOV and DOF of each will differ because of size and distance variances.

So f/8 gives different DOF on different formats primarily because of focal length, as well as frame size. Your Canon S31S's 1/2.5" sensor's diagonal and thus 'normal' focal length is ~7.2mm which on APS-C or FF is ultra-ultra-wide. (I'm looking at your cam's specs.) A 7mm lens on any of those frames has essentially infinite DOF, no matter whether the aperture is f/2.2 or f/22. So, comparing f/8 on 7mm vs 50mm lenses: the exposures are equivalent, while the FOVs are in different leagues.

QuoteQuote:
Regarding the 18-55mm kit lense. I don't recall ever using the optical zoom on the Canon - I just don't need it. I either get closer or crop and enlarge on the PC. So, for the K-r I'm thinking about 50mm lens, either the M type I have or buying an A type.
50mm is short tele on APS-C; 30mm is 'normal', and 24mm starts to be 'wide'. Their FOV equivalents on 135/FF would be 75mm, 45mm, and 36mm. I'll bet when you power-on your Canon, it defaults to its shortest focal length. On your S31S that's 6mm, FOV equivalent to 36mm on 135/FF, or 24mm on APS-C. Putting a 50mm lens on a Kr would give MUCH narrower FOV and MUCH thinner DOF. No, the cheap DA18-55 is much more appropriate for your shoots. But I still don't know why your S31S doesn't deliver for you.

QuoteQuote:
I hope you'll bear with me, because I'm sure that I'll have more questions as I think about this. I turned 80 last May and I have been taking pictures and even developing my own B&W film since back in the early 1950s.
I'm a bit younger, started developing not much later, and still have much to learn. And yeah, you should have kept your old Pentax gear! Ah well, so it goes...
11-06-2011, 03:20 PM   #10
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Opahujo, one other option is image (focus) stacking in software on a computer, take several images with different parts of the train layout in focus then stack and align them and use the in focus part of each image to create an image with all in focus. Do a Google search on focus stacking for instructions. You don't need expensive software PS Elements is one option. You can save yourself the cost of the lens

Hans

Last edited by hnikesch; 11-06-2011 at 03:39 PM.
11-07-2011, 11:49 AM   #11
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RioRico, first, thanks again for your patient explanation. It all seems so very logical, that is until I think about film cameras. I suspect digital cameras and how they work would be a lot easier for me to understand if I had never used a film camera. Sort of like my grandkids feeling much more comfortable with all the electronic gadges that are available these days than I am.

I also took your advice and ordered a K-r last night with the kit lens. I also orderd the rather expensive D-BH109 AA battery holder; but I like AA batteries and had good experience with the Copper Top ones. I buy 'em in quantity when they are 50cents a piece, and after their life in a camera I use them in PC mice.
QuoteQuote:
I'll bet when you power-on your Canon, it defaults to its shortest focal length. On your S31S that's 6mm
Yep, I checked and most of my photos were indeed taken at the 6mm focal length and also mostly at F/2.7 to F/4 and f/8 in the Av Mode. F/8 at a focal length of 6mm would indicate to me that the aperture has diameter of 0.75mm. That's pin-hole lens territory! I have seen some great work done with a home-made pin-hole disk, but here again is where my thinking about my experience with film cameras gets me in trouble, because 0.75mm aperture diameter sounds wrong to me. By the way, I once had a set of three lens extenders that I used with the P30T and a 50mm lens to get in tight and I got some great close-up shots.

About the S3IS, I looked at the shots of my 8'x14' train layout again and you're right, DoF is not the problem - the focus seems to be uniform - but the details suck, like the writing on the sides of the cars just isn't "crisp." The strange thing is that pictures of a group of people, close-ups for stuff I sell sometimes on e-Bay, or most other uses are fine.

Last edited by Opahujo; 11-08-2011 at 03:15 PM. Reason: grammar
11-07-2011, 04:02 PM   #12
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hnickesh, thanks for the suggestion. I have stitch software in my PC, but have not used it so far. Anyway, it doesn't look like there is a DOF problem - all the shots aren't as good as I think they should be, but it's not a matter that either near or far areas are clearly out of focus. I have played with about everything (lighting, exposure time and f stops, tripod of course, max. mega pixel,...) I could think of.
11-07-2011, 05:09 PM   #13
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QuoteOriginally posted by hnikesch Quote
Opahujo, one other option is image (focus) stacking in software on a computer, take several images with different parts of the train layout in focus then stack and align them and use the in focus part of each image to create an image with all in focus. Do a Google search on focus stacking for instructions. You don't need expensive software PS Elements is one option. You can save yourself the cost of the lens

Hans
I was about to suggest this same thinkg, I think "focus stacking" is your best answer in this case.
11-09-2011, 09:36 AM   #14
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QuoteOriginally posted by Opahujo Quote
F/8 at a focal length of 6mm would indicate to me that the aperture has diameter of 0.75mm. That's pin-hole lens territory! I have seen some great work done with a home-made pin-hole disk, but here again is where my thinking about my experience with film cameras gets me into trouble, because 0.75mm aperture diameter sounds wrong to me.
I hope it's OK to re-post my question. I have spent many hours reading about DOF, FOV, APS-C, crop factor, etc., and I am beginning to understand most of the differences between film and digital photography, but I still don't know the answer to the above question. Can someone help, please.

My K-r is on order! :-)))
11-09-2011, 12:01 PM   #15
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depth of field

QuoteOriginally posted by Adam Quote
Yes, they are usable (however, they will NOT give you more DOF than the kit lens, they will, however, give you less (i.e. produce blurred backgrounds) if they have faster apertures)

https://www.pentaxforums.com/forums/pentax-lens-articles/110657-how-use-meter...ml#post1140019
The maximum aperture of a lens has no effect on depth of field over any other lens of the same focal length when set to the same aperture such as f/4. A 50mm f/1.4 lens set to f/4 and a 50mm f/4 lens set wide open at f/4 will have identical depth of field. The 50 f/1.4 will exhibit less depth of field only when the aperture is increased above f/4.
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