SCT Reducer Corrector with a Maksutov Telescope - Strange Artefact Investigation

[@aroxchannel]

Thanks for posting this video. I have a 180mm Celestron Maksutov Cassegrain and I have done quite a bit of visual observing and astro-photography with the Celestron 0.63 focal reducer. I've never seen the kinds of aberrations you demonstrate here.

[@JenhamsAstro]

Thanks, that’s useful to know. I think there is a reflective surface somewhere in my setup but as yet I haven’t found the culprit.

[@petkog07]

Exact same problem on my 90mm Mak, no reducer and a dslr

[@Witscher]

Interesting. Thanks for sharing!

[@AntPDC]

Thank you for taking the time and trouble to identify the culprit, even though you weren't able to nail it. The comments I've seen on forums such as Cloudy Nights seem always to denigrate the Mak/Cass/focal reducer combo you have been trying to use here. Many opinions are given to explain why - some citing optical design theory far beyond the understanding of we amateur astronomers. However, were it possible easily and reliably to adapt Mak/Cass scopes to be faster than their native capability in the manner of SCT's, I think we would have seen such a product in the marketplace selling like hotcakes. We haven't.

[@JenhamsAstro]

Yes, the jury is still out. I'll make another video if I figure anything out, otherwise I'm more than happy with the 127 at f/12.

[@AntPDC]

@@JenhamsAstro I'm not sure it's a case of the jury still being out - more that this combo was convicted by the jury several years ago

[@JenhamsAstro]

@@AntPDC I wanted to try it as whilst I’ve read a lot of the negative feedback on the forums, some people give a positive review. For me it doesn’t work. On to the next!

[@AntPDC]

@@JenhamsAstro Experimentation is the very crucible of learning, I agree.

[@natem7440]

i have the Orion version of this Mak and a 0.63 FR - i will try this out too and see.

[@groundhoppingwlkp3622]

It works, but only good image field is smaller - around 12-13mm diagonal (on the center). If you crop it on APSC it's ok

[@jamesw5713]

I have used an Anteres f/6.3 SCT Reducer/Corrector for years with my Celestron 127 Mak without this issue. Saying that, I only use this reducer for astrophotography and not visual. Is it possible that you aren't using the correct back space distance when using it for visual?

[@fazergazer]

In my case it was reflections from the inside of the reducer extension tube and primary and secondary baffle tube like yours

[@JenhamsAstro]

Interesting thanks. After your comment I checked my camera adapter tube and it looks fine, nicely black.

[@LuiszDiaz]

What about to flock the internal/secondary tube? (not sure if that's a propper name) I oppened mine to see how is the light reflecting there and looks it could be the issue. I'll try in the next days with some opaque paper with mine

[@OurAmazingSkies]

Very interesting, I used to use a Celestron 0.63 FR with my Mak 127, I never noticed any problems except vigneting. I changed to a 2" 0.5 FR (Telescope Service) only because I wanted more reduction, I'm still using it now, I image variable stars (photometry) and it's perfect at the right focal distance of 55mm. Looking forward to your findings with another FR, I think the one you have maybe faulty.

[@JenhamsAstro]

I'll post another video if the culprit is finally confirmed.

[@Astronurd]

The reducer is not optically designed for the 127.

[@JenhamsAstro]

Very true, it was just an experiment that turned into a puzzle.

[@kymt8523]

I had the same internal reflection issue with a Celestron 6-in SCT + FR. In my case the artefacts were apparently caused by internal reflections off the extension tube rings between the FR and the camera. Swapping these out for another set I was able to eliminate the problem. Flocking the extension tube may be the solution. Good luck!

[@JenhamsAstro]

Thanks that's useful to know. My DSLR extension tube looks nicely black so I'm at a dead-end with the issue at the moment.

[@davido2644]

Can confirm, 6" sct + celestron focal reducer, but have not tested where the issue comes from, and it's been a while since I've encountered the issue, since I've not been observing bright targets.

[@Astroturf100]

Hi Graham this is a good mystery for sure. I have done the test visually looking at Venus and with primary baffle flocked only and it has helped me eliminate the flares in my 127 sky-watcher mak even at very high power. Wonder did you try a look without the reducer? Did you get an improvement visually at all? Thanks for posting this video.

[@JenhamsAstro]

I've had a good look without the reducer and I don't see the issue at all. Hopefully the baffling, which I'll leave in place, will lead to some benefits even at f/12, not sure. Tis puzzling.

[@Astroturf100]

@@JenhamsAstro I agree with your conclusion that its most likely the corrector reducer that is giving you the flares at the edges of your field of view. A pure reducer only will most likely do the trick for you. Unfortunately, these reducers can introduce spherical aberration and vignetting also, something to take note. But flocking is definitely worth doing and I do think that its giving you benefits; it sure did visually for me! Just for fun you should make a video comparing older footage compared to the same targets now that you have flocked the OTA and see if it made a difference.

[@BennyKleykens]

Thanks for investigating this further and risking damaging your gear! Does the flocking of the secondary help any with contrast of the scope because considering doing the same on mine.

[@dragosniculescu6877]

Years ago, I think that there was a focal reducer for Maks made by Intes Micro. But I'm not sure. I remember that I saw someone selling his Mak, an original Intes Micro, with a reducer which didn't look like other reducers I know. Did somebody know about this? About your experiments, it's very good you did it, even that the results are not good for now. You can try to defocus in both directions, to see what is happening. And on a less bright object.

[@JenhamsAstro]

I haven't seen that reducer but I've heard of it, it makes sense to use a bespoke unit if one is available. I will keep experimenting as Venus was a convenient but tough target given its extreme brightness. I saw no issues after swapping out the reducer and going back to f/12 though.

[@GTheoMedia]

I wonder if the reducer will do the same artifacts with the Maksutov 102/1300 version.

[@JenhamsAstro]

Worth a try if you have a reducer already, but I wouldn’t buy one especially to test it.

[@dedskin1]

The problem is that any kind of reflector can not handle big eye pieces , i noticed it on 4inch Newtonian and 30mm eye piece , and there was no improvement over 25mm , i got 5mm of tube visible, this is due to the light path , secondary mirror being a problem narrowing the field of view where on Refractors i could put in 50mm EP on a classic 80mm scope . So when we fit a reducer in we get like larger field of view and Macs are known to be sharper because they have smaller central obstruction but this is where the problem is , now it has larger then designed FOV and somewhere in there there is a problem , its not the faulty reducer , its not a faulty scope , its the design it self . If you have put the Full Frame on there i guess something strange would happpen . Even more drastic then this . Because its limited field of view , most limited FOV of all scopes is the MAC. So smith cassegrain barely escapes , Newtonian escapes but not from the EPs larger then Full frame sensors , but refractor , you can put a medium format camera on it , all you will get is vignetting , its just the light path and the optical design . Field of view obstructions . You can see this if you put no EP , and let it twist the image and reflect it on the wall . There you would see the light cone , or illuminated space being different in different designs .

[@MrWacha]

I think I may have a culprit but this is just a hypothesis for now. Try changing your Celestron #93633-A Adapter to anything in M48 size and see the difference. I was just affected by those arcs after moving from M48 extender and Baader Click-lock SCT visual back I used yesterday to this Celestron 50mm long T-Adapter I see you are using as well. Let me know if this solved your issue. I have no flocking paper nor black matt paint on me to blacken this adapter for testing as I just came up with this finding. Will buy some from Amazon and test. PLMK how this goes for you if you had a chance before me. [Edit] just to add I'm on C5 SCT + Telescope Service F/6.3 FR/Corrector (same as Celestron one) and the only thing common to your setup is this bloody adapter, so it can't be coincidence. I seen the very same thing on my Meade 90ETX MAK way back. I was using same adapter there but I though as you that those reducers and MAKs don't go well together.

[@JenhamsAstro]

Interesting. When I look into the adapter it looks dark, with the recessed lens electrical contacts being the only obvious source of reflection. But it isn’t as non-reflecting as the newly flocked secondary , so maybe that is it.

[@MrWacha]

@@JenhamsAstro I'm not using DSLR, so no electrical contacts for me to cause any reflections. I think this is to do with the difference in diameters between FR and extension tube where adapter has this flat part making contact with FR flange. My 533 MC cam has smaller sensor vs DSLR hence those arcs are less pronounced, yet they still are there if bright star is just off the FoV. I am purchasing M48 50mm long SCT extender to make imaging train. Will let you know if this helped as much as other setup I mentioned earlier.

[@Seafox0011]

Great tests! Will be following your lead with my own Mak too. There's some speculation that there's a difference between the 'China' made version of the f/6.3 FR versus an older 'Japan' made variant.

[@JenhamsAstro]

Thanks. I read some talk about the different versions. Hard to be sure.

[@tilenoman1265]

Hello, I know it's been quite a long time since you posted this, but have you been able to figure out anything about these strange artefacts?

[@JenhamsAstro]

Not satisfactorily. Others have commented that the wider field is “allowing” a reflection from the adapter to reach the sensor. This seems plausible but I haven’t proved it.

[@tilenoman1265]

@@JenhamsAstro Thanks for the reply. I guess yeah. By the way, which adapter/tube are you using to connect the T-ring to the reducer? I'm probably going to try this option too, just not sure what to go for completely. Is it 2" or 1,25"?

[@JenhamsAstro]

@@tilenoman1265I used a Celestron SCT T-adapter, model 93633-A

[@AviF]

Would it be worth trying an EdgeHD (8?) reducer if it fits? Since they reduce but don't correct? I'm wondering if anyone has tried that before.

[@groundhoppingwlkp3622]

No, EDGE have other reducer (0.7) so using 0,63 with it won't work

[@Mrcloc]

😬 You could have marked the OTA with the corrector cell and just unscrewed the cell. You're very brave to remove the corrector from the cell... But I'm absolutely sure it'll be fine. Thank you for this! I think because you get the aberrations only when the reducer is on, it must be the reducer. Perhaps the lens edges of the reducer aren't blackened?

[@JenhamsAstro]

I think it's a reflection issue somewhere - others have suggested in the adapter - so maybe the reducer is just revealing it rather than causing it. I'll have another go at figuring it out at some point. So far the 127 seems to have gone back together OK!

[@MountainFisher]

I do not do any serious photography with my 127 Mak, I use an F7 102 ED triplet refractor. I don't like adding to mine other than using a two inch diagonal with wide angle eyepieces to 62° to 72° fov at 37x to 50x. One I got came with the 1.25 diagonal, pissed me off. Eyepieces were freaking Kellners too, should of bought the Celestron version at least they're Plossls. edit; I least I think they are.

[@JenhamsAstro]

I really like the 127 for planetary, but like you I've got faster scopes for other targets. I thought it was worth an experiment though.

[@MountainFisher]

@@JenhamsAstro Yes I suppose it couldn't hurt, but focal reducers are not cheap though. If I already had one it would be worth a try, but I wouldn't buy one with my other scopes, an F5 1/12th wave 150mm reflector, the F7 refractor and a Sky Watcher 102 and 127 Maksutov. I have noticed neither one of my Maks has the clarity of my other 2 scopes. I suppose if I hadn't had my 150's mirror refigured it wouldn't be in the same class as my 102 Apo.

[@mesenteria]

I am firmly convinced of a number of matters here. Firstly, both baffles could stand to be shortened by about one full cm.....at least. But even if you shudder at the the thought, their tips, especially the faces of the ends, need to be blackened and made dull, probably best by applying Musou black paint (amazon). The secondary baffle flares out quite a bit and ends up occluding the light path to the central part of the primary mirror. Cutting the secondary baffle back, or tugging it off altogether, will almost certainly not have a deleterious effect, especially at night, and especially if...bringing up my last point...you use a fairly long dew shield, at least as long as the aperture. This one item will prevent incident light, say from a bright moon just outside of the field of view, from making ghosting and flaring.

[@JenhamsAstro]

That’s interesting. As you say I’m not keen on testing it on my 127!

[@bill5982]

I was going to suggest the same idea of using a long dew shield.

[@groundhoppingwlkp3622]

I bought similar 0,63 celestron reducer for my Mak127. I had only 2 nights to test it, so it's not a full review but I can say something ;) 1. Mak 127 gives APSC field of view (nearly), so with 0,63 reducer it will be 0,63x times smaller - so around 4/3 matrix. For smaller cameras like ZWO 585 it would be optimal vigniette free. 2. I had also small problem with focus shift (due to celestron sct - t2 nipple) but yes, stars only in center of FOV are good. Going further from ten center of image they are more elongated. 3. I haven't similar patterns like on the film, but I didn't tested it on Pleaides or other bright stars, so I'll check it. To sum up - for smaller fov (like 1 inch and so) it works, but don't expect miracles, you won't win APOD with Mak F8 combination, stil for amateur work it's ok ;)

[@JenhamsAstro]

Thanks for adding your experience. I’m hoping to pin down the source of the reflections at some stage as my example of very bright stars near the edge of the field was a tough test. I’ve since seen not dissimilar artefacts with a different setup - likely the reducer just ‘allows’ these to reach the sensor. The distortions are another story, so it’s a 6 out of 10 from me.

[@groundhoppingwlkp3622]

@@JenhamsAstro ok finally I had good weather so tested that spikes with reducer on Pleiades. On 10s exposure (around F8 and 1000 mm) I see it only on autostretched images in Siril. Also they are a bit smaller. When I see where yours spikes are I can definitely say that it's field curvature problem. Stars near center don't have it, only these on the outside. So just use 0,63 reducer with smaller sensors like ZWO ASI 585 and smaller ones and it shouldn't be any problem :)

[@heavyjohnny]

The celestron reducer is a paper weight. Toss it in the rubbish and cut your losses. Starizona make a the SCT corrector which is a game changer.

[@JenhamsAstro]

Good to know thanks. £450 here unfortunately.

[@heavyjohnny]

@@JenhamsAstro it turned my SCT 9.25 into an edge hd. Field of View is flat from edge to edge. It’s worth every penny

[@MM0IMC]

Rather "baffling". 🙄

[@JenhamsAstro]

Indeed!