So... given the success I have had with the old manual focus Super Takumar 200 f/4 and Pentacon 135 f/2.8 I decided to see if I could find myself a dirt cheap old manual 300mm+ lens. I had a few options to look at, but several times in researching those other lenses I repeatedly saw comments comparing them to the Soviet erra Tair-3 long lens. Everything I read indicated that: 1) the Tair-3 is optically good
2) the Tair-3 is very large and heavy
Heavy long lenses may be an issue for hand-held daylight photography, but this is astrophotography! Surely the lens would weigh similar to a small APO, and that is no problem at all... right?
So I found a Tair-3a m42 mount version on ebay and ordered it! Last night I defied the clear sky chart and spend the dark hours using holes in the passing clouds to do a test sequence on the lens. Short version? I am happy!
Lens Details:
- The aperture iris of this lens has quite a lot of blades. Makes for a tight grouping of a large number of spikes off bright stars (I like the effect). It also has a nifty double-setting system for the iris. First ring is an outer-stop position that sets the maximum amount you can stop down - this ring has notches at 1/2 stop intervals. The second ring controls the iris and has no notches at all, allowing free setting of any iris position from wide-open to whatever stop you set on the first ring.
- Focus on my lens requires more force then I would expect with a modern lens, but I have found that no impediment to achieving critical focus.
- This is a "Long Lens" rather then a Telephoto, in a way it has optically more in common with an APO scope then a Telephoto lens! I believe it is a three element design (doublet + third element further back in the tube).
- The Tair-3A is set up as a standard camera lens, while the Tair-3S is set up for a funky riffle-stock type mount for handheld photography. The 3A is may be easier to focus in small increments. This lens is a Tair-3A.
Performance notes:
- Wide open at f/4.5 the lens performs passably, but not perfect. Stars at the edges are slightly distorted and there is an center-directed blue flare off of brighter stars. I should note that the performance when wide open is better then the *best* performance from some cheap modern zooms I have used!
- At f/5.6 things are looking very good, stars are still not *PERFECT* at the corners, but already quite a lot better then many APO+flatteners can produce!
- At f/6.7 stars are round across the whole field and slightly shaper then f/5.6. The blue flare on bright stars is gone. A *very* slight red halo shows up on my moded 350D if the focus is a bit off, so perfect focus is important (but when is perfect focus *NOT* important!)
- At f/8 the stars *might* be just a very slight bit shaper still, but not enough to make up for the loss of light gathering power.
- I found that with my lens if you are not careful with how you tighten the tripod collar you can create a situation where you can not quite reach infinity focus. Once I figured that out though it is very easy to avoid.
Edit: Looking closely at the stars in the wide open test and specifically how they are not quite the same in each corner I have a feeling that part of the off-round shape may have a lot to do with the very likely years of rough treatment this lens has endured - it is possible a better condition copy will be even better!
Test image info:
To test the lens I decided to point far south at M8 and M20. The result is a nice image, but I wish I had selected a field with more bright stars in view to really test the optics! To create these test exposures I used the Baader UV/IR modified Canon 350D auto-guided on the CI-700 mount. I used no Darks and no Flats. I used Nebulosity to align&stack and performed identical background neutralization and histogram stretch operations on each image in PixInsight. I shot:
- 4x 60s exposures at f/4.5
- 4x 60s exposures at f/4.8
- 4x 90s exposures at f/5.6
- 14x 120s exposures at f/6.7
- 1x 180s exposure at f/8
Attached is the forum-sized full frame result of the f/6.7 exposure stack. I intend to re-do this image with proper calibration later and will post that in another thread later (including high res full frame image). I boosted the saturation on this image only.
