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Old M42 lenses on a modern CMOS astrocam? What toils may exist and is it a good idea?


pipnina

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My telescope being out of action for a while has led me to look at potential low cost optical replacements to tide me over. This is where I learned of old camera lenses with M42 fittings, and even lenses intended for 120 format film. These are remarkably cheap and some old threads on here have shown that they are quite capable, even if they are not necessarily up to modern standards in all regards.

With that in mind, all of the threads back then spoke of attaching them to DSLRs, which makes sense as adapters for the bayonet fittings would be more commonly desired for terrestrial photographers. However when attaching them to an astrocam I suspect it may lead to more headache? Mostly I would think when it comes to backfocus and or the need for a tripod thread to exist somewhere. Even longer lenses (135, 150, 200mm fl eg) seem to lack a tripod foot, which would leave my astrocam and lens pair with no suitable method of being secured to my mount save for tactical application of cellotape haha.

Are there any here using such a setup today? All the old threads are from 2010 to 2013 and perhaps the tastes for cheapo lenses have changed.

There is a film photography shop in Plymouth which i have visited and has a wide range of lenses and camera bodies, I intend to pay them a visit if there is a possibility of making this work!

Cheers

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8 minutes ago, pipnina said:

Are there any here using such a setup today? All the old threads are from 2010 to 2013 and perhaps the tastes for cheapo lenses have changed.

They do not work, please save yourself any pain and send me any old M42 lenses you have or see and I will "dispose" them for you. 🤣

I use a 200mm and 300mm Pentax SMC Takumar M42 lens on my ZWO cameras and they work fine. You can get away with T2 extension tubes as they screw into the M42 1mm pitch thread of the camera lens just enough to hold a-ok. There are M42 1mm pitch to T2 0.75mm pitch thread adaptors but I've never had the need.

I have read that P-SMC-T 50mm lenses work well too. The beauty of old M42 lenses is you can manual focus and adjust the aperture. In truth a modern Canon 50mm will be better but you can't control the aperture manually or focus easily unless you build an interface to control the lens off camera (Arduino examples on the net). I have also used old Canon FD lenses as I have a number still and they are ok but not as good as modern glass - you have to stop them down a few stops.

I think a lot of people still use them for widefield narrow band imaging.

Using old lenses reduced I feel when prices started to shoot up (advent of video in DSLRs and later mirrorless cameras too). Good ones with no fog/fungus can no longer be found for pennies in reality.

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Not all M42 are the same :D

There is M42x0.75 and there is M42x1mm. Former is T2 thread and later is well M42 thread. You can't securely screw one onto another and you'll need adapter to attach lens to camera.

With most of those lenses you'll need to stop them down to F/4 even if they are faster, and they are not particularly sharp as far as stars go.

Your best bet is to decide on FL you want to use and then get lens that is x2 or x3 longer focal length. Then when you shoot - you will bin your data x2 or x3 as lenses are simply not sharp for modern small pixels. They want pixels in range of 9-12um or larger to give sharper image.

Even modern lenses are not up to task with small pixels. I played around with Helios 58mm f/2 lens and ended up getting Samyang 85mm to give me ~50mm "feel" with small pixels (I use split debayer on ASI178 and then bin once more x2 which turns 2.4um pixels into 9.6um ones).

BTW, here is example of image taken with 58mm Helios:

veil.thumb.jpeg.44a5796c856e6a322ab9da08570843fc.jpeg

Well, I did not bother to process it particularly well - it is just B/W (not debayered, just binned) - image of Veil nebula, 1h total exposure from Bortle 7/8 sky with ASI178 color cooled.

Lens was stopped to F/4, but even with that stars are soft and bloated - not particularly sharp (and there is diffraction thing on bright stars).

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Another one with the 135 and 200mm Asahi Pentax Takumars, they work reasonably well once you make the infinity focus adjustment on them but you'll have to bear in mind they are designed to focus red, green and blue at different focus points so your post processing and expectations have to adjust for it. In terms of mounting I've found the three screw type telescope rings are quite versatile as you can use them to hold the lens and camera.

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Aye, the 3 screw style guide scope mounts work well for smaller lenses.  Had good results also with a 200mm takumar SMC and a Tair 3 (not quite as good imho) in terms of image quality.  Tair 3 I use with 90mm tube rings with some home made 3D printed spacers.

I use mine with a m42x1 to cannon adapter then a canon filter holder from zwo which gives the correct focus distance for my camera.

I adjusted the infinity stop on both my lenses and it was easy, but I've had one where it wouldnt reach infinity even on a canon DSLR and I could not adjust the infinity stop as the screws were stuck fast.

Edited by Ratlet
Clarify what I use for each lens
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It's probably worth saying that whilst these aren't optimised for astro imaging, you can pick up a lens for £40-£60 for a takumar or tair.  Do you get £40 worth of astroinmaging out of a takumar 200mm?  I'd say so.

1907732497_HeartNebulanotbad.jpg.22a9543ebb25d1f29f53d7a0cfe17b99.jpg

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That's a great image. They're definitely worth a go and the perseverance/reward does pay off, but if you want no nonsense and future proofing and can afford to, id recommend get a Samyang 135mm and be done with it.

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27 minutes ago, happy-kat said:

If you already have one why not use your guide scope

The guidescope is, sadly, most likely worse than a lot of lenses 😕 It's fine for guiding but I'm only using a 6x4mm sensor for that, it has a 1.25" camera side connection and I have an APS-C sensor.

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