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Coronado PST imaging focus issues with ZWO 224MC or DSLR


Elp
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Hi, been trying a few times to image with a Coronado PST and cannot get focus.

With the ZWO 224MC I tried printing a "low profile nosepiece" found on the internet and that didn't work - the camera looks like it needs to go further into the eyepiece holder - some people have managed to get it to work I don't know how. So I modelled another low profile nosepiece which has a 4mm depth groove around the bottom of the nosepiece face so it can sink into the Coronado eyepiece holder 4mm more - nope still no focus. People have suggested unscrewing the lens part of a barlow out and using that with the camera nosepiece, tried a 2x Meade telenegative and a generic 5x - nope makes it worse.

So today I tried a DSLR connected to a t nosepiece extension tube and ran into the same issues. I don't know how people are managing to image with this scope - I know it's not designed to be imaged with but it is something I wish to do considering others have managed it.

On another note, how clear is surface detail visually on a PST, I can manage to see sunspots but no light/dark granular structure, with the focus ring dialled all the way to the left I can see prominances, sunspots with the ring dialled more to the right though most of the time its all a red blur - checked the ITF and that's clear (it's the newer type PST).

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Yeah I know, what I want to avoid. It's why I modified the low profile eyepiece I modelled to allow at least 4mm of that 5mm, doesn't look like I can make it deeper due to internals of the 224mc.

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I used to own a PST several years ago and could not reach focus with anything but an eyepiece.
I believe the focus issues depended on when/where the scope was made, but others will know more.
Certainly at the time nobody seemed to presenting good solutions.
The best solution I found at the time is shown in the pic.

Baader Hyperion eyepiece + Baader camera adapter + T to camera adapter + DSLR.

Hopefully you will find an easier solution.

Clear Skies, David.

 

Hyperion Camera.jpg

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I do a bit of imaging with my Coronado PST, using an ASI 290MM Mini cam (mono) and 2x Barlow. I've also had good results with a QHY5-II Mono. You should be able to get reasonable results with yours.

They key advantage of the 290MM Mini and the QHY5 is that they fit entirely in the eyepiece holder so that you can get focus, which the DSLR was never able to manage without a barlow. The DSLR was also way too big and cumbersome. I also found that imaging with a colour camera just didn't work - I found focussing the bright red image nearly impossible, and the resultant colour image was never satisfactory.

This is a quick capture from this afternoon. About 500 frames captured with Firecapture with the ASI 290MM Mini and 2x Barlow, plus a bit of colour tweaking in Photoshop. This is nearly the full frame view. You do get a bit of gradient across the field which you can get rid of with flats, but it doesn't really bother me. I think it gives a more 3d effect.

51498937367_67eb787304_h.jpg

51499995083_eb1021b6ca_b.jpg

Edited by lukebl
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Merlin - thanks for that, makes for a good read.

David - seen a similar setup yesterday so been looking out for a zoom eyepiece with a threaded top - this might be what I'll currently have to do.

Luke, I have the following barlows (see image) and non were able to get me focus. Some people have suggested remove the lens and use that with the camera but I don't see how that works as the lens outer diameter is the same size as the camera nosepiece O/D (unless people mean use the blank barlow housing with the camera - that would mean pushing the camera sensor further away from focus?), only the Meade and the SVbony have easily removable lenses.

I suspect the 290mm mini is a different kettle of fish compared to the 224mc regarding sensor back focus as well as being mono - see image below of the issues with the 224mc camera. Standard nosepiece has a step in it which pushes the sensor focal point too far back, the second low profile eyepiece (credit to yvmo) is supposed to alleviate that but I still stuggle with focus, the third nosepiece I designed with a 5mm depth channel which allows the sensor to be up to 5mm more "into" the Coronado eyepiece holder, still doesn't focus, some people have managed with a 120mc so my 224mc should also work. Your point about colour sensor may be the issue, I use OACapture and turn all the auto settings off as I noticed they were blowing out details when they were on. My uploaded image of the sun is the best i've captured with a low profile nosepiece as a one off session, there's a lot of noise in the image and nothing like the surface detail you are getting - visually I don't see anything like your images which I suspect I won't - I can only visually see prominences tuned one way and sunspots tuned the other, no surface detail whatsoever - my ITF is clear.

Barlows.JPG

ZWO 224 nosepieces.jpg

Solar 07-09-21 Halpha - copy.jpg

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  • 7 months later...

Thought I'd update this.

Since the last post I've acquired a zwo 290mm mini, and a Celestron Omni 2x Barlow of which the lens element screws off. With one ring on the front of the 290, the Barlow lens element screws directly into it, and with the following positioning in the Coronado I managed to get some sort of focus:

1218923089_DSC_24242.thumb.JPG.db410c0b6029bfffbaa51cc22894ef21.JPG

 

And the composite image, strange as I managed to image both the surface detail and the prominences separately with the same setting on the tuning ring all the way to the left but with different camera settings. Setting the ring more to the right didn't reveal any more surface detail and the prominences disappear. 

Other than that happy how the image turned out:

1417554823_Sun-14-05-22-HaCoronadoPST-doimg-Copy_070559.thumb.jpg.9fb703debffa0853bb41a1c31f7f820a.jpg

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