Baader MPC MK3 spacing

[edarter]

Hi,
Having been out of astronomy for about 18 months I'm trying to get back in to it but I'm having some issues with the astro photography side of things. At the point I stopped I was trying to get the required 57.5mm spacing to the sensor on my astro modified EOS600D when using a standard 48mm camera adaptor (Not the Baader one). The advice kindly given at the time was to buy an old 48mm camera filter and remove the glass as this would add the required 2-3mm. I've done that but from all the measurements I've done this seems to add more than 3mm! It looks like it adds 5mm. I initially thought I had just bought a filter who's body was too long but when I compare its dimensions to a Baader spacer ring (bought in error a while ago) they are the same! I've also looked at buying one of these: https://www.teleskop-express.de/shop/product_info.php/language/en/info/p6435 despite them being eye wateringly expensive. But looking through the specs of this its also adding 5mm rather than the 2-3 that I need. I'm completely stumped and any help would be greatly appreciated!!
This is what I have, as you can see I have 59.9mm with the filter ring fitted and 54.9mm without :

[mikeyj1]

when i was setting mine up with a canon 1300d, i needed 55mm spacing, not 57.5mm (and +-0.5mm was ok apparently).  not sure if one of us is wrong, but i don't get coma now...

here's my post

 

[spillage]

can you not just add t2 extensions between the filter and the mpcc?

[John78]

https://www.firstlightoptics.com/adapters/baader-t2-delrin-spacer-ring-set.html

I believe you need 55mm + 1/3 of the thickness of any filters in the optical path between the coma corrector and camera.

[spillage]

Is the 55mm to the t2 thread and 57.5 to the m48. But yes you do need to remember to add in the thickness of the filter. as @John78 has mentioned Delrin rings will also help with fine adjustments, but get i near enough and take some test shots and you can then fine tune the distance.

[John78]

32 minutes ago, spillage said:

Is the 55mm to the t2 thread and 57.5 to the m48. But yes you do need to remember to add in the thickness of the filter. as @John78 has mentioned Delrin rings will also help with fine adjustments, but get i near enough and take some test shots and you can then fine tune the distance.

Oh yes I see - so the easiest option is get a T2 camera adapter and simply screw the CC into that with a spacer as required, or 3d print up some M48 spacers.

There a few UK sellers on a well known auction site selling the EOS T-rings for less than £6.

[edarter]

Thanks for the replies everyone. I would prefer to use the m48 as it apparently lets in more light, but I don't use any other filters at the moment,  so if my understanding is right I think i am indeed still 3mm too long?

[alacant]

7 hours ago, edarter said:

I have 59.9mm with the filter ring fitted

This is because you still have the t2 adaptor fitted. Unscrew it first! Now screw the glassless filter into the exposed m48 male thread on the cc and thence the remaining male thread of the filter ring into the t adaptor.

HTH

[edarter]

4 hours ago, alacant said:

This is because you still have the t2 adaptor fitted. Unscrew it first! Now screw the glassless filter into the exposed m48 male thread on the cc and thence the remaining male thread of the filter ring into the t adaptor.

HTH

Which bit is the T2 adaptor? I'm really hoping its just a case of me missing something silly like this! The adaptor in my photo is a 48mm one and I can't see anything obvious that comes off either that or the cc

[alacant]

6 hours ago, edarter said:

Which bit is the T2 adaptor?

**Assuming you've found vignetting...?

The collar on the bottom (in your photo) of the coma corrector. It has two slots in it to enable you to insert a blade to unscrew it. Your 5mm filter is too much. File 1mm from the knurled side; easy to use sandpaper and rub the ring against the paper on a flat surface rotating the ring randomly.

If you can get a bank loan, you can get the real thing.

HTH

[edarter]

Thanks alacant, that's making more sense now! I never realised that this part can / should come off when used with the 48mm adaptor! Sounds like I need to reduce the height of the filter ring regardless though. What I don't understand is that the part you have linked to appears to add 5mm to the optical path as well, the same as the filter ring I have, so I'm not sure if it will help or not. Its technical description mentions 3mm and 5mm.

[alacant]

8 hours ago, edarter said:

the part you have linked to appears to add 5mm to the optical path

Hi. No. It adds 3mm. The thread is 2mm which disappears into the female of the adaptor. This gives you exactly the 57.5 you -theorectically- need. Over APS-c on my reflector, I found I needed 4mm, hence my initial suggestion of a low profile -4mm- filter ring.

Recommendation: Try with the 5mm ring first. It takes only a few minutes to sand it down. Even better, join a club where between them, members will be able to loan or supply you with all manner of m48 spacers without your having to resort to metalwork.

HTH and clear skies.

[Spaced Out]

I had this same issue with spacing an M48 ring, see here....

Alacant solved this one for me !  ?

I sorted this problem by removing everything (including T2 threads) from the MPCC. Then I added this 4mm spacer.....

https://www.aliexpress.com/item/Lengthened-bucket-S8031-M48-lengthen-20-mm/32251614997.html?ws_ab_test=searchweb0_0,searchweb201602_1_10065_10068_10130_318_10547_319_10548_10696_450_10192_10190_10084_10083_10618_452_535_534_533_10307_10820_532_10301_10821_10303_204_10059_10884_323_10887_100031_320_10103_448_449,searchweb201603_60,ppcSwitch_0&algo_expid=80a30881-692f-460e-9758-a9eb068c3934-0&algo_pvid=80a30881-692f-460e-9758-a9eb068c3934

Then I fine tuned the spacing with some baader T2 delrin spacers. These T2 spacers are too small for M48 but if you cut them with scissors and stretch them slightly then they do fit. I just added a single 0.6mm delrin spacer to the 4mm spacer and that seemed to do the trick for me.

https://www.firstlightoptics.com/adapters/baader-t2-delrin-spacer-ring-set.html

HTH

[edarter]

Guys - thank you so much, I get it now! I will give the sanding down option a go first and see how that goes. Think I'll purchase some delrin spacers as well so I have that option ready for when the clouds clear
I should indeed consider joining a club as well, something I have long put off due to time issues but I think it needs to be done.

Cheers

Ed