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04-11-2014, 01:15 AM   #1
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SMC Takumar M42 135mm F2.5 for astrophotography?

135mm seems to be the sweet spot where you get maximum magnification before either the speed drops off or the cost goes through the roof. I am looking at this lens as a potential candidate for astrophotography as it seems to be far cheaper that the K version and reportedly better than most of the M and A variants:
Specifically the later 6 element SMC version.
Super-Multi-Coated TAKUMAR/Super-Takumar 135mm F2.5 Reviews - M42 Screwmount Telephoto Primes - Pentax Lens Reviews & Lens Database
I can't seem to find any reviews that specifically mention coma distortion towards the edges and a real clear idea of how it would behave for this purpose near wide open. I would be mostly using it closer to wide open and stopped down to maybe F4 if I put together a barn door tracker.

Unless someone has another suggestion that is. I already have a M50 1.7 on the way for its reported super flat focus field for wide angle stuff, but I would like something at least twice the magnification.

04-11-2014, 09:02 PM   #2
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I have seen a fairly comprehensive comparison of the K135/3.5 that recommended it highly over the M version, specifically for astrophotography. It would be really helpful if I could remember where. The K135/3.5 is the same design as the Super-Multi-Coated 135mm f3.5, which is fairly cheap. The comparison suggested to me that more elements were not absolutely necessary for astro. The K and Takumar 135/3.5s are only 4/4.

That may suggest the Takumar Bayonet, but I saw some pretty soft corners on mine. So I wouldn't encourage that.

A really quick series with a Pentax-A 135mm f2.8 looks like this lens is also at least worth a look. Again, only about half an answer, sorry.
04-12-2014, 12:44 AM - 1 Like   #3
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An old test on film
04-12-2014, 08:32 PM   #4
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Wow if that test is accurate I see what you mean about the the K135 F3.5. It has an amazing lack of coma and flare around the light sources in even a wide open corner. That's the lens I'm looking for then, thanks guys.
EDIT: Would still love the F2.5 version though, it looks like it might be useable wide open too and an extra stop means a lot when looking at stars, twice the price is a bit much for me though.

Last edited by PPPPPP42; 04-13-2014 at 06:13 AM.

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