M42 or M48

[RustyShackleford]

Hi,

Newbie question...

Ive just received my mount and scope today and I'm having a go setting up but Ive realized by t mount doesn't attach to the reducer Ive purchased.

Its an evostar 72ed with a reducer/flatterer with a M48 connection but my existing t mount is m42.

I'm going to purchase either a new M42 adapter for the reducer or a M48 T mount. so basically I can be all M42 or all M48.

The adapter is slightly more expensive but only about £10 so its not a deal breaker but I was wondering what the difference is and if it will be best to go with M42 or M48 and what sort of difference it will make for imaging?

Thanks.

[vlaiv]

I'm a bit confused what is your problem.

First let's figure out what your connections are and then we can see what sort of adapters do you need. Also bear in mind that M42 usually refers to 42mm x 1mm metric thread which is different than T2 thread which is 42mm x 0.75mm - pitch is different.

Most of astronomical gear uses in fact T2 mount while some older photography lenses use M42 mount - don't confuse the two.

Focuser has (possibly) a thread - what is it?

Flattener will have front - scope facing thread and rear - camera facing thread - which ones are they?

Your camera will have thread on it - which one is it? (most likely it is T2 thread unless you have very large camera).

Do you use any other accessories like filter wheel, OAG or anything like that?

Since reducer/flattener operate at certain distance - it is also important to know this distance and to know sensor distance from camera thread. What sort of camera are we talking about?

[RustyShackleford]

Hi Vlaiv,

I'm confused myself so apologies if I haven't explained properly

The camera is a Nikon D3400.

This is the t mount i currently have that I use to attach to 8" dob.
https://www.rothervalleyoptics.co.uk/TMN.html

This is the reducer I have - bought this to attach camera to evostar 72ED.
https://www.firstlightoptics.com/stellamira-telescopes/stellamira-2-0-8x-reducer-field-flattener-with-m48-adapter.html

So I have the reducer slotted into the scope but the t mount doesnt fit. Ive attached pictures of the reducer with the cap removed and then the next part removed (I think thats the adapter but might be wrong?) I assumed the t mount would connect when the cap was removed. The other side of the reducer goes into the scope and fits fine. unless Ive got it all mixed up.

 

[vlaiv]

Ah, ok.

From what I can see on FLO website for that FF/FR - it has M48 on both sides - scope side (2" filter thread is M48 - so you can connect it to scope via threaded connection if you focuser supports it - that is good to avoid tilt), and it has M48 on camera side - together with "M42 tread" which could be T2 thread actually rather than M42 thread.

From your image I see that adapter included - screwed in its place in second image. Check if that is indeed T2 thread - take it off and screw just it to T2/Nikon adapter that you already have. Be very gentle and don't force it - if thread has different pitch you should not be able to screw it in more than half a turn to a turn. If you can screw it in multiple turns and it screws in easily - then it is matching thread and it is in fact T2 adapter - then you should be all set.

At least I think so - you would be for Canon camera as it has lens mount that requires 55mm of distance and canon adapters are made like that - and it matches perfectly to distance required by this FF/FR.

As far as I can see  - Nikon F-mount has this distance at 46.5mm and if your adapter adds 8.5mm of optical path - you should be ok to exactly 55mm - unfortunately I can't see info on the link you provided, it does not say optical length of that adapter.

 

[RustyShackleford]

Hi Vlaiv,

I tried as you suggested, removed the adapter and tried it against the nikon adapter but its too big. The outside diameter of the nikon adapter is just about the same size as the diameter of the threads on the reducer with the adapter removed.

[vlaiv]

20 minutes ago, RustyShackleford said:

Hi Vlaiv,

I tried as you suggested, removed the adapter and tried it against the nikon adapter but its too big. The outside diameter of the nikon adapter is just about the same size as the diameter of the threads on the reducer with the adapter removed.

I think I was not clear enough.

I meant that you try little thing that you removed not M48 thread. I was hoping you will figure out if smaller bit has T2 or M42 thread on it. If it has T2 thread - then it should fit without any issues.

Don't try field flattener on DSLR adapter - but rather than little thing that screws into field flattener.

[RustyShackleford]

ah right. No, it doesnt fit. the nikon adapter is too small.

[vlaiv]

3 minutes ago, RustyShackleford said:

ah right. No, it doesnt fit. the nikon adapter is too small.

Are you sure? Same adapter you used to attach your camera to 8" dob?.

I was probably not clear again sorry - let me try one more time - this time I won't try to explain it with words.

Try to screw this thread:

in here:

Both should be 42mm wide, and only reason can be thread pitch - it will start to screw in but will stop after a half a turn to a turn (if that happen don't force it, you can damage the thread).

[RustyShackleford]

Yeah, I just measured them with a ruler (I should have thought to do that sooner).

The outside of the thread on picture one is 48mm and the inside of the thread on picture two (the nikon adapter) is 42mm.

[RustyShackleford]

oh and yeah, same adapter I use to attach to the dob.

[vlaiv]

1 minute ago, RustyShackleford said:

Yeah, I just measured them with a ruler (I should have thought to do that sooner).

The outside of the thread on picture one is 48mm and the inside of the thread on picture two (the nikon adapter) is 42mm.

Ok, now I'm confused again - you attached two pictures - first one - showing what I believed to be M48 thread and unscrewed bit - this one:

and then this image - with that attachment screwed in place:

I was suggesting to try screwing that possible T2 thread (which is obviously smaller in diameter than M48) into your DSLR adapter and to see if it will screw in.

[RustyShackleford]

no, the first pic that you've labelled m48 measures 54mm. the second one that youve labelled t2 measures 48mm and the nikon adapter measures 42mm

 

[MarcusH]

13 hours ago, RustyShackleford said:

I'm going to purchase either a new M42 adapter for the reducer or a M48 T mount. so basically I can be all M42 or all M48.

If I understand your original question correctly, you are pondering if you should buy the optional StellaMira M42 / T Adapter for your flattener/reducer or if you just should replace the T / M42<->Nikon adapter that you currently have with an M48<->Nikon. Correct ?

Imaging-vise that really doesn't matter, both will work on your current setup (APS-C). What you might want to consider is possibly future proofing your setup. Do you see yourself buying a dedicated astro-camera at some time in the future ? As @vlaiv said those are usually T2 (except the big, full frame ones) so you then would need a way to reduce the M48 to T2 anyway. As the backfocus is only 55 mm, any possible addition to the imaging train (filterwheel / OAG / adapters / etc.) is going to have preciously little room so a "drop down" to T2 right at the reducer might be a good choice.

The best advice would probably be to have a chat with the guys at @FLO. Once they know your current setup and your long-time goals, I'm sure they can suggest the best solution for you.

[vlaiv]

11 hours ago, RustyShackleford said:

no, the first pic that you've labelled m48 measures 54mm. the second one that youve labelled t2 measures 48mm and the nikon adapter measures 42mm

 

Ok, I get it now

M54 is used for very large cameras and is one of "standard" threads.

Best thing to do is to get yourself M48 Nikon lens adapter like this one, provided it adds only 8.5mm of optical path:

https://www.rothervalleyoptics.co.uk/rother-valley-optics-m48-t-mount.html

But do check first with them if it has required optical path. If not, you can purchase ultra short Nikon adapter and then use M48 extension rings to get proper distance.

Or get this one:

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p3629_TS-Optics-T-Ring-from-M48-to-NIKON-Bajonet.html

as it has proper optical length:

(btw what is show on image looks exactly the same as adapter at RVO so there is a good chance that one being 8.5mm also).

[RustyShackleford]

Thanks Guys. and thanks for the patience. No doubt I'll be back with more questions but I'm going to get the m48 nokia mount.

[RustyShackleford]

just quick update. the nikon m48 mount arrived and it all fits together now just need to wait for the weather to change so I can get it outside now!