Lens: Spiratone 35 mm f/3.5 enlarging lens
Vintage: uncertain - 60's or 70's?
Lens Mount: M39.
Needed Adapters: This lens is easy to adapt to most cameras and just requires an M39 adapter. I just screw the lens into the backside of the adapter instead of the front (normal way). This does make adjusting the aperture a little more difficult (since it will be inside the bellows when the lens is mounted. Just have to do it before you mount the lens onto the bellows.
Preferred Mounting: Reversed.
Filter Thread: About 27mm.
Street Price: About $5 in good used condition. Prices vary a lot online, shop around.
Controls: Aperture setting.
Aperture: 5 blades.
Basic Function: Requires a bellows to set focus and magnification
| Extension | Magnification | Working Distance |
| 5 cm | 1.70 | 48 mm |
| 9 cm | 2.84 | 40 mm |
| 13 cm | 4.00 | 36 mm |
| 19 cm | 5.71 | 33 mm |
| Est. Focal Length: 34.8 mm | ||
Appearance:
Resolution vs. Aperture:
The sharpest aperture is f/4 and the most resolving aperture is f/4. I prefer to use f/4 for most images because of the sharpness and resolution. You could also argue for using f/5.6 (at least at lower magnification) because of the improved corner sharpness with little loss in resolution (see next section).
Corner Sharpness vs. Aperture:
The corner performance of this lens is only so-so at the sharpest aperture of f/4. At higher magnification, f/4 improves enough to not be a problem. If you want improved corner sharpness, f/5.6 is a good compromise.
(Testing done at 1.7:1 magnification. Numbers at each aperture setting will tend to improve as the magnification is increased and worsen as the magnification is decreased).
Sharpness and Resolution vs. Magnification:
This lens shows decent sharpness and resolution across its usable magnification range of 1.7x - 5.7x. Compared to other lenses in its magnification range - better quality enlarging lenses, bellows lenses - this lens does not tend to produce as good sharpness and resolution.
This lens has so-so corner performance at f/4, but it does improve as the magnification increases.
At maximum magnification, this lens can resolve details down to about 2um.
Performance: Sharpness vs. Magnification:
I have 4 lines that represent levels of performance from outstanding (top) to fair (bottom). This shows where this lens fits into the hierarchy that I have created.
The Spiratone 35/3.5 shows sharpness performance varying from good at low magnification to poor at its higher end. Especially at higher magnification, other lenses will perform significantly better.
Performance: Resolution vs. Magnification:
I have 4 lines that represent levels of performance from outstanding (top) to fair (bottom). This shows where this lens fits into the hierarchy that I have created.
The Spiratone 35/3.5 shows resolution performance varying from very good at low magnification to fair at its higher end. Especially at higher magnification, other lenses will perform significantly better.
Resolving Power vs. Magnification:
This graph represents the smallest details that are able to be resolved by this lens at various magnificaitons. If the number doesn't get smaller as the magnification rises, there is little benefit to going up in magnificaiton with this lens. This situation is also called empty magnification.
Good resolution, no problems.
Chromatic Aberration:
This lens shows minimal color fringing in the center and even better on the periphery (0.010 - 0.040%). Less than 0.04% is considered insignificant. This lens shows mild longitudinal CA on out of focus details (see image below). Not bad for $5.
Longitudinal CA:
Image Contrast: Image contrast is not the strong suit of this lens. I think that this may be the price of a $5 lens. The elements don't appear to be coated like higher quality lenses will be. This problem can be mostly fixed in post-processing.
Flare: There is mild flare present with this lens during testing. Again, probably the result of no/minimal lens coatings. Careful masking of stray light is essential.
Distortion: This lens shows no significant distortion during testing.
Image Samples:
About 2.5:1 magnification, f/4, focus stack of 25 images, resized:
Pixel level crop from the image above:
OK pixel level detail for the magnification, but a little softness is present.
About 5:1 magnification, f/4, stack of 29 images, resized:
Pixel level crop from the image above:
Getting quite fuzzy at the pixel level. Doesn't look bad when resized to a normal size image.
Conclusion:
This is a fairly easy to find lens that tends to be cheap (I paid $5, free shipping). For the price, you can't do much better. If you are willing to pay a little more, a good quality used short focal length enlarging lens will perform significantly better in terns of resolution, sharpness. It is easy to adapt to a bellows with an M39 adapter.
This lens has so-so to good corner performance at the sharpest aperture of f/4, although stopping down to f/5.6 will improve the number significantly with little loss in resolution. This lens has extremely good CA performance in the corners. It has very little longitudinal CA on out-of-focus details - better than I was expecting.
The main two flaws of this lens are probably both related to the lack of lens coatings - a little flare and relatively low contrast. The contrast is mostly correctable with post-processing. The flare can be lessened with careful lighting and masking of stray light. This lens has a magnification range of about 1.7:1 to 5.7:1 on a bellows. That means a narrow depth of field and will generally require focus stacking.
Despite the flaws, the images that you can produce with this $5 lens are perfectly acceptable. If you have a few more dollars (say $25 - $35), a used 35 mm Schneider enlarging lens will significantly outperform this lens.