Using M42 camera lenses with a cooled astrocam.

[Phil]

Hi there,

I am looking for a way to attach a couple of manual M42 lenses to my ZWO ASI071 Pro camera. I know from an old thread on here that the flange focal distance for the M42 lens system is 45.46mm. My camera has a sensor depth of 17.5mm and my filter draw is 21mm wide. This leaves 6.96mm for an M42x1.0 female to M42x0.75 adapter to allow my lens to be screwed into the back of the filter drawer. The only adapters I can find add 7mm to the focal train.

Has any one tried doing this and will the additional 0.04 mm of length make images taken with my 200mm F/3.5 Takumar look noticeably out of focus?

Thanks,

Phil 

  

[Enceladus Dan]

Hello Phil,

I have 200mm and 400mm m42 lens which I've used with eos adaptor on my 600D. I've just got my first astro cam and only tried it so far with baader variable spacer and focused on distant object in the day. 

For your case 6.96mm, from memory when i was looking up uses of m42 lenses, I think it's better to be slightly under than over. Being over can stop you reaching infinity focus. (Anyone - If I remembered wrong please correct me). You can get small spacers to put over m42 threads ro add fine tuning. 

https://www.firstlightoptics.com/adapters/baader-t2-delrin-spacer-ring-set.html which can get you close with a 5mm M42 extension. 

 

Clear skies

Danny

[Anthonyexmouth]

1 hour ago, Phil said:

Hi there,

I am looking for a way to attach a couple of manual M42 lenses to my ZWO ASI071 Pro camera. I know from an old thread on here that the flange focal distance for the M42 lens system is 45.46mm. My camera has a sensor depth of 17.5mm and my filter draw is 21mm wide. This leaves 6.96mm for an M42x1.0 female to M42x0.75 adapter to allow my lens to be screwed into the back of the filter drawer. The only adapters I can find add 7mm to the focal train.

Has any one tried doing this and will the additional 0.04 mm of length make images taken with my 200mm F/3.5 Takumar look noticeably out of focus?

Thanks,

Phil 

  

You can get a cheap set of extenders on amazon and then tweak the distance with delrin rings

[Phil]

My problem is not increasing the distance, it would already be too long. The problem is finding an M42x0.75(T2) to M42x1.0 adapter that adds less than 7mm to the optical path. I already have a set delrin spacer rings but to use them I need a shorter adapter.

[Oddsocks]

4 hours ago, Phil said:

My problem is not increasing the distance, it would already be too long. The problem is finding an M42x0.75(T2) to M42x1.0 adapter that adds less than 7mm to the optical path. I already have a set delrin spacer rings but to use them I need a shorter adapter.

Phil.

Don’t forget, when calculating the back-focus distance that adding filter glass in the optical path pushes the focal point (between the filter and the camera) further back by an amount roughly equal to 1/3 the filter thickness. If you use 2mm thick filters in the drawer the focal point will be ~0.66 mm further out and you would probably need to add one or more fine delrin spacers to reach focus, even with the 7mm adaptor.

Edited March 11, 2023 by Oddsocks

[Ratlet]

Best bet is to give it a try if you have everything.  The infinity focus on older camera lenses can be badly set so it can be a little too close or a little too far away.  I've had lenses which reach focus on my setup and lenses that don't.  I go m42 lens-canon ef adapter-zwo canon filter drawer-cooled camera and with that the spacing should be perfect, but it rarely is.  Some lenses won't get to infinity, some just make it to infinity and others travel a good bit past.

If you can't reach infinity focus then you could try sanding the female end of the adapter (0.04mm is a tiny amount) or alternatively you could adjust the infinity stop of the lens.  On some lenses the adjustment requires serious surgery (taking lens elements out to reach the adjustment screws) but on others it's relatively easy.  For example the takumar 200mm F4 has 3 screws on the focuser barrel which can be loosened allowing it to be adjusted.

Edited March 11, 2023 by Ratlet

[michael8554]

Hi Phil

As Danny said, so long as it's under (or over, I can't remember either) the lens will reach infinity-focus before the infinity mark is reached.

But 0.04 mm is so small I hope it doesn't matter.

Michael

 

[Enceladus Dan]

16 hours ago, Phil said:

My problem is not increasing the distance, it would already be too long. The problem is finding an M42x0.75(T2) to M42x1.0 adapter that adds less than 7mm to the optical path. I already have a set delrin spacer rings but to use them I need a shorter adapter.

I thought you were trying to find 6.96mm between the adaptor and camera, I didn't realise that's what you have left to find the adapter. 

As Ratlet says, give it a try first. You may be lucky to get enough to reach infinity, if not his idea of sanding the adaptor down slightly sounds much better than the drama of opening up the lens to move the hard stop. The idea of performing lens surgery was what made me check and double check before I got my lenses, if I was able to use them on my DSLR. 

Clear skies 

Danny

[Clarkey]

On 10/03/2023 at 21:29, Phil said:

My problem is not increasing the distance, it would already be too long. The problem is finding an M42x0.75(T2) to M42x1.0 adapter that adds less than 7mm to the optical path. I already have a set delrin spacer rings but to use them I need a shorter adapter.

I found some on fleabay from China. I can't remember the exact specification, but I used them to put my M42 lenses on my astro camera. I'll check the size when I am at home, but I'm certain they add less than 7mm.

[Clarkey]

OK found it. The adaptor is one of these:

T2 Male Astronomical Telescope Adapter T2 Male Thread To M48X0.75mm NDE | eBay

The outside thread is M48x0.75 and the inside is M42x0.75 (T2). The other end is M42x1 to attach to the camera. If you exclude the thread depth on the camera side, the depth is just under 6mm so should work. Alternately if you use the M48 connection it will not add any length to the imaging train as both threads will be used.

[Ratlet]

1 hour ago, Clarkey said:

OK found it. The adaptor is one of these:

T2 Male Astronomical Telescope Adapter T2 Male Thread To M48X0.75mm NDE | eBay

The outside thread is M48x0.75 and the inside is M42x0.75 (T2). The other end is M42x1 to attach to the camera. If you exclude the thread depth on the camera side, the depth is just under 6mm so should work. Alternately if you use the M48 connection it will not add any length to the imaging train as both threads will be used.

BRILLIANT.  I've been looking for one of these for ages.  Got a couple of lenses that I couldn't adjust the infinity focus and this will sort that out.  Cheers dude!

[Phil]

On 13/03/2023 at 08:45, Clarkey said:

OK found it. The adaptor is one of these:

T2 Male Astronomical Telescope Adapter T2 Male Thread To M48X0.75mm NDE | eBay

The outside thread is M48x0.75 and the inside is M42x0.75 (T2). The other end is M42x1 to attach to the camera. If you exclude the thread depth on the camera side, the depth is just under 6mm so should work. Alternately if you use the M48 connection it will not add any length to the imaging train as both threads will be used.

Thanks for this. I'll take a look. Also got somone hopefully quoting for making the same.