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It might be worth checking your source for this particular Ishihara test. I've just done a 12-sample Ishihara test online and, as usual, saw every figure. I'm certainly not colour blind but, in this, I can't see a letter or number so I think it tests for something else.  There are control tests with nothing in them and also tests in which only a colour blind person will distinguish a figure. A good while ago I took UCLAN's Introduction to Astronomy distance learning course.  One of the tasks was to rank ten naked eye stars from red to blue. I was surprised to find I got the order right (ie in accordance with spectral class) apart from inverting one adjacent pair near the middle.  This makes me think that your vision may have a limitation but, to be sure, I'd go to a dark site with a few other people who know the sky well enough to be sure you were all talking about the same star! Very big apertures are not the best for star colour in my experience. A reflector is the most reliable on colour and being out of focus slightly helps to spread the colour and diminish the brightness. Olly Edit: Sorry, I missed the later posts and the test problem has already been resolved.

Thanks Rick, this is my intent too. But first, I want to understand HOW it works and the necessary bits and pieces for the 'simple' work :D. With AP, it's never easy :)) As I mentioned, I am complete beginner in AP, and a bit confused.  Thank you and everyone for your suggestions, it really helped me a lot to make an idea of what's going on.

Seems a shame after all that work to get it right. Sell it and use the money to get something you want to do the job.

Does this one work? Can I remove the extension and use the short T - ring and correnct it into my telescope?

Hi, I started deep sky astrophotography a few years ago now and still feel fairly new to this very complex hobby (although with the UK weather, that's probably only a couple of weeks worth of actual experience 😂) and have spent the past year or so looking at upgrading my whole setup, and hope that those with more experience can see if it all sounds ok and that nothing clashes with each other or if you think that something else would work better etc. (I currently own everything I need for the autoguiding side of things)   Here's what I have come up with: Scope: Explore Scientific ED APO 102mm Carbon (FL: 714mm - FR: F/7) Flattener: TS 2" 0.8x Reducer / Flattener for 100-102mm f/7 Refractors (as recommended by Astrobackyard) Mount: iOptron GEM28 (1.75" LiteRoc Tripod + iPolar) Camera: ZWO ASI 294MM-PRO (2x2 4.6um or 1x1 2.3um) NB Filters: Baader Narrow Band Filter Set - CMOS Optimised (1.25" Ha, Oiii, Sii - 6.5nm) FW: ZWO Mini EFW Extras: ZWO ASIAIR Plus - ZWO EAF - some sort of portable power supply (12v 5a)   Specs: Scope - FL: 714mm @f/7 (571mm @f/5.6 with 0.8x flattener/reducer) Triplet APO FCD-100 glass Camera - M4/3 Sensor - 11.7MP, 4.63um, 14 bit, RN: 1.26e, FW: 66K, QE: 90% (2x2 bin as standard) for 102mm scope  - or -  47MP, 2.3um, 12 bit, RN: 2.7e, FW: 14K, QE: 90% (un-binned) for small refractor/lens. Mount - Max Payload: 12.7kg (roughly 10kg for AP as advised by FLO) - scope with all attachments etc. comes to roughly 5.5kg   Why?: Scope - I chose the scope as I love the quality to price ratio and it's wide FOV - the extra £200 for the carbon I think is a good to have with the much reduced total weight of 3.3kg! (which is handy for the lower payload mount) and it looks cool of course 😁 Flattener - I'm not sure on the flattener, there doesn't seem to be one designed specifically for the scope that's not ridiculously priced - Astrobackyard used this one when he had the same scope. Mount - I like the light weight/portability of it with it only weighing 4.5kg and can still take a large payload considering (also plenty of payload for scope/attachments). Camera - I chose this as I like the ability to be able to switch bin modes - the bigger 4.63um pixel size for the 102mm scope and smaller 2.3um for my WO Z61 and Samyang 135mm lens. It's almost like having two cameras. FW - The small filter wheel was due to only using 3x 1.25" NB filters (colour with Sony A7iii for now) and for the Samyang lens it would be better with a smaller setup.   I think that's everything... as you can see, this is quite a lot of money to be spending so that's why it would help me if someone with much more experience could check before I buy everything to put my mind at rest! Thanks, Dean