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02-27-2021, 09:50 AM   #1
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Macro lens on K1 to digitize 645 B/W negs

Hi all,

I have a K1 and I'm wanting to convert 120 and 220 B/W negatives to digital. I have a Plustek scanner for my 35mm negs and slides and would like to try using my K1 with a good lens instead of buying a flat bed scanner for my medium format work. My challenge is that my current lenses (DFA 28-70 f/2.8, FA 50 f/1.4) won't fill the entire sensor frame at their minimum focus setting. I can't focus close enough if I do fill the frame. I clearly need a macro lens. How can I calculate or can anyone tell me which focal length would best fill the frame without having to be 10 feet away? The attached image shows my proof of concept. The FA 80-320mm provides a useable image but at 320mm and this distance, a neg fills only approx. 1/2 the frame. Thank you!

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02-27-2021, 10:24 AM   #2
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1:1 macro lens should be enough for 645 negatives?
02-27-2021, 10:26 AM   #3
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If you're looking at single shot per frame, and especially if you work with larger than 645, I'd get a 50mm lens, though you already have a 50mm. Maybe an extension tube for the FA 50 would be enough, and also much cheaper than a new lens? I scan 35mm film with K1+100mm wr, and the working distance is comfortable at 1:1 pointed down to a desk. I'm not so sure for ~1:2 that 645 film would require, and personally I wouldn't want to walk back and forth like in your photo, with the vertical setup I finish a roll in a few minutes once it's setup. 100mm would allow you to stitch multiple 1:1 shots per negative to maximize resolution.

Last edited by aaacb; 02-27-2021 at 10:32 AM.
02-27-2021, 10:32 AM   #4
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A 100mm macro should do the trick. Maybe roughly 10-18 inches from the front of the lens, depending on the lens.

One of the older 50mm macros with 1:2 (0.5) magnification (Pentax A or earlier) with maybe 5-8 inches from the front of lens.

If you have deep pockets you could buy the Pentax Film Duplicator - they make one for 45 film too. But you probably still need to buy a lens.

https://www.ricoh-imaging.eu/eu_en/pentax-film-duplicator-with-mount-holder-24x36

02-27-2021, 10:56 AM   #5
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As your target is flat, you need a flat field macro lens, which is not always the case.
A lens that is not prone to PF will be preferable.
Vignetting is also a parameter to take into account, if you plan to fill the frame with the neg.
Rather short focal lenghts (about 50mm) are generally preferable but I'd say that a 100mm could fit the bill.

I will NOT recommend a Pentax 100mm, as they are prone to PF.
02-27-2021, 11:03 AM   #6
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I do occasionally digitize medium format negatives using just a light table and my camera on a tripod pointing down. My 50mm macro has been the one with the most practical working distance for the K-1, working on a table. The D-FA50mm macro works really well and provides full pixel-shift resolution into the corners and great contrast, no need for extensive masking on the light table, still advisable though. For pixel-shift, and thus electronic shutter, I need to use an ND filter, so that the flickering of the fluorescent light table lamps with magnetic ballast (100Hz here, 120Hz in the USA) is averaged out by several seconds of exposure time.

With a 100mm, I need to put the light table on the floor (or on top of some box) and again my tripod over it, but that's not as comfortable an not as easy to keep clean - one of the main concerns.
02-27-2021, 11:45 AM   #7
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QuoteOriginally posted by JensE Quote
With a 100mm, I need to put the light table on the floor (or on top of some box) and again my tripod over it, but that's not as comfortable an not as easy to keep clean - one of the main concerns.
Let the ImageSync app be your friend. Having the extra working space between is helpful as is a boom/horizontal arm on the tripod so it's easily set up behind your light box and work area.
02-27-2021, 12:02 PM - 1 Like   #8
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First off, I would convert to a vertical arrangement. You want the camera sensor plane to be parallel to your subject and it's a lot easier to obtain this way than guessing with a tripod. In this arrangement, the light box and subject are flat (check with a bulls-eye bubble level) and the camera is positioned above it looking directly down. Using a remote trip on your camera will help for ease of exposure and also for eliminating vibrations. There are copy mounts available, but you might be able to build your own since they're pretty straight forward. Before starting, place a small mirror across the front of your lens and place a pinhole light source at the center of your subject position. Adjust your camera mount until the light is reflected directly back to the pinhole. This will align your camera. Then, adjust focus (previously adjusting distance to get the desired frame-fill), and shoot away. You can most likely get away without any further focus adjustments if your results are coming out sharp. It makes changing your subject material a lot easier and you can use a flat piece of plate glass to place on top of your subject to keep it flat. Gravity will do the rest.


You probably have the lenses needed although as mentioned, you won't get the best results without a lens designed for macro shooting, but stopped down with extension tubes, your existing options will probably work pretty well. One issue that might give you trouble is if you use a zoom lens, depending on the lens, it may tend to "creep" in this arrangement. You might have to secure the zoom adjustment to prevent this.


Last edited by Bob 256; 02-27-2021 at 02:26 PM.
02-27-2021, 12:29 PM   #9
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QuoteOriginally posted by Bob 256 Quote
clamp the zoom adjustment
Some tape usually works to keep the zoom ring in place.
02-27-2021, 12:38 PM - 1 Like   #10
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QuoteOriginally posted by MikeinNY Quote
I clearly need a macro lens. How can I calculate or can anyone tell me which focal length would best fill the frame without having to be 10 feet away?
A macro lens might help, but figuring out working that will will fill the frame can be a pain. Here are a few points:
  • Since the 645 negative is a bit more than twice the size of 35mm, you know that the target magnification is somewhere around 0.5x (1:2)
  • 645 frame size is 56x41.5mm, so the challenge is to fit the 41.5mm side into the 24mm dimension of the K-1's sensor, meaning 0.578x magnification (1:1.73). Assuming a block focus prime, the amount of extension from the mount flange should be 1.73 times the focal length minus 45.5mm flange distance.
  • Working distance will depend on lens focal length and length of lens from flange with extension
A 50mm macro lens allowing 0.5x (1:2) would work nicely as might your choice of 50mm lens along with a 35mm or 40mm extension tube. A focus rail will make life easier once magnification is dialed in.


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02-27-2021, 01:39 PM   #11
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QuoteOriginally posted by JensE Quote
so that the flickering of the fluorescent light table lamps
Unless those are some special kind of fluorescent lights, you ought to be using something else! You are likely to get some funny colors in your copies. See this shot of a CFL spectrum.



Incandescent bulbs would be best (although perhaps with a heat problem), and most LEDs will be better than CFLs (but you might still have a flicker problem for short exposure times).
02-27-2021, 01:44 PM   #12
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QuoteOriginally posted by AstroDave Quote
Unless those are some special kind of fluorescent lights, you ought to be using something else! You are likely to get some funny colors in your copies. See this shot of a CFL spectrum.



Incandescent bulbs would be best (although perhaps with a heat problem), and most LEDs will be better than CFLs (but you might still have a flicker problem for short exposure times).
Diffused flash?


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02-27-2021, 01:56 PM   #13
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QuoteOriginally posted by tryphon4 Quote
A lens that is not prone to PF will be preferable.
Sorry, but what is PF ?
02-27-2021, 02:39 PM   #14
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Your only source of light should be the light box preferably masked only to show the image being copied. All the room lights should be out or really subdued. Otherwise, you'll get front surface reflections which can cause artifacts in your copies.

As AstroDave mentioned, florescent lighting is a poor choice (with the exception of some cold cathode tubes), but white LEDs with a high CRI (color rendering index - above 80) can work well. Use a slower shutter (1/4 second or so) and flicker issues won't happen (in many cases, LEDs run off DC and don't flicker). Some LED systems allow you to open the shutter and make the exposure by strobing the LEDs (using the camera's flash sync) which works really well and produces consistent exposures based on the strobe time.
02-27-2021, 02:41 PM   #15
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QuoteOriginally posted by stevebrot Quote
Diffused flash?
Probably better than CFL. Guess I'll have to take some spectrum measurements of my flash guns!
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