[TAP]

Hey Pentaxians,

I use my Pentax DSLR to digitally scan paintings and artwork for clients at work.
The process involves shooting the artwork in segments, and stitching them together in post.
This allows the artwork to be printed quite large (I did a 4ft x 5ft print recently) at full resolution.
My clients are very satisfied with the results, but I know there's room to improve.

I want to achieve the sharpest overall images possible with the limited resources at my disposal.

A Little Background:
I Currently use my SMC Tak 50mm/1.4, or my SMC Pentax-F 50mm/1.4 (both at f/5.6)
Because of the crop factor, these equate to about 75mm on my k-5.

Questions

1. Is this the most suitable aperture to achieve best overall sharpness with these lenses?
   
2. (Assuming sharpness gets worse toward the edge of the frame) should I be shooting more frames and cropping them down to avoid losing detail?
   
3. I've heard that "art lenses" are not the best for overall sharpness. I have the (SMC Tak 35mm/2) and the (SMC Tak 55mm/1.8). Would either of these better suit my needs?

With my current setup, I can't go much longer than a 55mm without having to tear down a wall.


Any other suggestions/advice/input is very much welcome. I wouldn't be the photographer I am today if it weren't for these forums, and I'll gladly accept any information you can offer that will help me continue to improve.


All the best,

Pat

[Kozlok]

If this is a big part of your photographic work, I'd look to the DA40Limited. It has nearly no distortion, and has about the most even sharpness across the frame of any lens. Super color rendition is another bonus. It is modestly priced (for a Ltd). Lots to love about it for this application.

On APS-C, most lenses have peak sharpness around F5.6.

[UncleVanya]

If this is a big part of your photographic work, I'd look to the DA40Limited. It has nearly no distortion, and has about the most even sharpness across the frame of any lens. Super color rendition is another bonus. It is modestly priced (for a Ltd). Lots to love about it for this application.

On APS-C, most lenses have peak sharpness around F5.6.

The DA 40 XS actually had more even sharpness across the whole frame in this shootout: Pentax DA 35mm F2.4 vs 40mm XS vs 40mm Limited Review - Introduction | PentaxForums.com Reviews

Also if the current method is stitching; then I don't understand why a longer lens can't be used. It seems like it should work just by increasing the number of shots used to stitch thus increasing overall resolution.

[dms]

I have never done a critical comparison--all I can say is I copied a lot of paintings with a 50mm f/1.8 Alpa Kern Macro Switar and a Nikon 55mm f/2.8 micro--both at about f/5.6, and felt the results were very good. (They are both considered to be superb lenses.) Always on T64 slide film.

My feeling is a good macro (Nikon calls it micro) provides better results at the closer distance--namely flat field image and no linear distortion--than regular (non-telephoto) lenses that are optimized for infinity. I especially think (in principle) a 50mm f/1.4 is not likely to be a flat field image for relatively close up work. Generally closed down 2-3 stops should be the best lens performance for a moderate speed macro type lens.

The 55mm Takumar is likely a very good lens for this type of work--not first hand experience--but generally moderately fast (symmetric) 50mm lenses are good macro's on extension--so it should do better in your scenario.

Also I have the 35mm f/2 (K which is the same optics), and while I have not used it close up, I use it quite a bit for low light-theatre work, and my gut feeling/impression is it likely will be a poor choice. Actually it seems to be made for speed and is not (otherwise) a great lens.

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Last edited by dms; 02-18-2015 at 10:24 PM.

[pacerr]

You might consider a dedicated macro lens. The SMC 50 f/4 perhaps or one of the newer 50-60mm AF macros. A 'normal' lens is presumed to be used for subjects from a few feet to infinity. The optical formula for that sort of lens has a 'plane-of-focus' that is equi-distant to all points -- essentially curved like the inside of a sphere.

A macro lens is designed to more effectively focus on a flat plane which is presumed to be much closer to the lens which describes your task. The better enlarger lenses may have the same characteristics for obvious reasons.

At a distance, depth of field helps overcome the curved 'plane' of focus of 'normal' lenses. DoF close to the camera becomes more critical when the distance to the corners of the image are proportionally greater than to its center.

If you can envision the effect of curvature of field in front of the camera you can imagine the same effect at the plane of the sensor, although on a micro scale. The macro optical formula inherently tends to optimize both front and rear planes for flatter focal planes and target subjects.

The other consideration is that the longer the FL (i.e., the farther you are from the subject) the flatter the plane of focus will appear relative to DoF so stitching a few images from a longer standoff range should provide a truer flat subject image.

On the other hand, just how critical is it? If your clients are happy as it is . . . well, just ask 'em if they'd fund the new lens.

I used close-up and macro photography at work for many years and unless the object was to scale measurements from the photos (which then included a scale reference) absolute imagery was never required.

[vonBaloney]

+1 for using macro lens (flat field, keeps edges sharp)

[K-Three]

I routinely copy my wife's artwork, I have both the DA100 2.8 Macro and the DA 35 2.8 Macro, I use either depending on the size of the piece. Mostly the 100 just to keep a decent working distance,
But, I'm not stitching, just single shots of each piece, usually the pieces are between 11x14 and 20x24, anything smaller we throw on the scanner.

You may want to look at one of the macros, 35, 50, 100, for better edge sharpness and flatter field lenses. For what you are doing, the old M and A lenses (50 & 100) may be a bargain way to try a macro lens,

How much overlap do you allow now? I've had some experience with combining aerial photos (just the lab part not shooting them) and those would be shot with about 1/3 overlap on the edges, we would cut off the overlapping edges and paste them up to create larger maps, with multiple passes, you only use about the middle third of each image.

Your technique sounds interesting,
How do you keep the camera parallel to the art work? That is my biggest pain setting up to copy my wife's work, keeping it all aligned for focus and to prevent keystoneing of the image, and that is working with a static condition, where the camera (tripod) and the art (attached to wall) stay put.
Are you moving the camera or the art? What about your lighting, does it move with the camera, or do you light the whole piece and leave it alone as you shoot?

I usually stop down to ƒ/8 when I want optimum sharpness.

[civiletti]

I suggest a macro lens for its flatter plane of focus. A process lens is even better, but would be totally manual and need mount adaption.

[interested_observer]

Evening,

Your questions - SMC Tak 50mm/1.4, or my SMC Pentax-F 50mm/1.4 (both at f/5.6)

• Is this the most suitable aperture to achieve best overall sharpness with these lenses? For the F50/1.4, it would be f5.6 across the entire face of the lens based on the review at

  • Pentax SMC-FA 50mm f/1.4 - Review / Lab Test Report - Analysis & Verdict

  I was not able to find a data based review for the Tak 50/f1.4 but I am going to assume that it too would be close to f5.6
• (Assuming sharpness gets worse toward the edge of the frame) should I be shooting more frames and cropping them down to avoid losing detail? If you were to move the edge of the picture to off the edge of the lens, more towards the center, you would avoid most of the problems.
• I've heard that "art lenses" are not the best for overall sharpness. I have the (SMC Tak 35mm/2) and the (SMC Tak 55mm/1.8). Would either of these better suit my needs? Others can probably answer better than I can.

You are already very experienced in this. If you are considering getting a bit more adventurous (read a bit more work initially), then there is - or now was, one gentleman here on the forum up to a while ago -RioRico, who was famous for looking for the absolutely best optical approach to things - and the lower the cost the better. Unfortunately, his eyesight is failing, so he is really no longer posting. That said, his legacy posts are still here on the forum for your reading. Also, he had something like well beyond 4K+ likes, so his advice was very well respected. I'll post a number of links to his suggestions, a bit further down.

So, what I think what Rico would write, would be something along the following....

You are really interested in reproducing a flat work of art, rather than something 3D. The best type of lenses for this would then be adapted enlarger lenses. With the demise of film, you should be able to pick up an excellent enlarger lens of the highest quality for a song. The trick would be selecting the right one, that could be adapted to a Pentax K mount. As I understand, there are quite a few enlarger lenses that use either the M42 or M39 lens mount - which just happens to be supported by Pentax (the old Pentax screw mount is the M42, and there is also a M39 to M42 adapter). You will also need a way to focus the enlarger lens, and that is done with a M42 helicoil.

I personally have never done it, but I have had several occasions of needing to do off the wall optical stuff at work, and the folks at B&H Photo in NYC have always been wonderful in helping. Here are the links that I promised that Rico posted that address enlarger lenses for flat work....

• https://www.pentaxforums.com/forums/22-pentax-camera-field-accessories/189416...ml#post1989876
• https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/174400-pent...ml#post1813524
• https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/162247-lba-...ml#post1692687
• https://www.pentaxforums.com/forums/54-pentax-lens-articles/152336-cheap-macr...ml#post1583483
• Shooting with a Pentax K10D: M42 Focusing Helical
• Lens Bubbles: Using Enlarging Lenses with a Focusing Helicoid on Sony NEX

You can use the search function (advanced) here and just use his name and enlarger lenses in the subject

[RAART]

I suggest a macro lens for its flatter plane of focus. A process lens is even better, but would be totally manual and need mount adaption.

+1 what he said... As you used already MF lens I guess it wouldn't be a problem for you if you get Enlarger lens in your desired focal length but as mention you need focusing helicoid and mount adaptation. I think that those having the best flat field and sharpness across. The problem is that also the those also don't get cheap today unless you are lucky and find the seller who does not have clue what he is selling...

[bassek]

My wife uses the Sigma EX 15-30 or the FA43 for her paintings depending on the size and space. Sometimes even the F35-105.
She did also use the Sigma EX 24-60 but did not like the color tint of that lens.

Seb

[MartinsB]

For precise reproduction purposes macro lenses are the first choise because of flat field, sharpness uniformity accross field and minimized aberrations. For your needs I suggest 35 macro Limited (no matter which version - SMC or HD) - this is a macro lens with normal angle of view on current Pentax APS-C cameras and with exceptional sharpness. Especially given that you are photographing paintings that are flat objects, the other lenses with more"artistic" rendering don't show their strengths and may have some disadvantages because of close distances.

[DevKom]

+1 for the 35mm macro Ltd for the reasons already detailed - including your limited space. Yes to using the the central area of the frames in your stitching, so I imagine the edges of the artwork would be mid-frame for those areas. One thing to emphasize, although it has been mentioned, is having the plane of the camera as square as possible to the plane of the artwork at all times to both ensure optimum focus as well as minimise perspective distortion. This means a good solid tripod and using bubble levels. I sometimes used to use a Hasselblad SWC (superwide) for artwork copying - as a rectilinear lens it was brilliant - but keeping everything level was paramount...

[UncleVanya]

I'm still confused - most of the time limited working distance is an issue due to either minimum focus distance or angle of view. If you are stitching then the field of view only seems to determine how many images you have to stitch. It seems like the 100mm f/2.8 Macro lenses would be possible but may not be ideal if I misunderstood your shooting constraints.

[Kerrowdown]

+1 for using macro lens (flat field, keeps edges sharp)

+2, exactly what I was going to suggest... but in this instance got beaten to the post.