Hi there,
I recently bought the Askar 103 Apo with all three optional reducers/flatteners. I have been really happy with the performance of the scope except for 0.6x reducer. My pictures have had signifcant chromatic abberation in the corners. I knew to expect at least some abberaton since it is nearly halving the focal length but I was hoping it would be a bit better.
I'm curious to hear if anyone else has had similar or different experiences?
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I purchased the same items. Last week I installed the 0.6x reducer to test.
I was very disappointed with the stars, even halfway to the center of the field. I quickly removed it and reinstalled the 0.8x reducer to resume my nights shooting. I am afraid the 0.6x will be in its original box, sitting on the shelf.
I will say that I am very happy with the 0.8x reducer. It does a great job.
Don
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The test I have seen indicated an excess of violet color in blue stars.
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I have had quite good results with the 0.6x reducer and an aps-c dslr as you can assess in the link below. The baader mod filter is a little more restrictive at the blue end than the ir cut in most imx571 cameras like the asi2600mc. If you have a camera like that you could try the astronomik L3 ir-cut filter to see if that helps. https://stargazerslounge.com/topic/415628-m31-with-askar-103apo-and-06x-reducer/#comment-4431781 |
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I figure you would have to have two different lenses of either fluorite or extra low dispersion glass in order to get really low focal length ratio refractor and either a triplet or petzval design to not use other things to have acceptable levels of low chromatic aberration in the photos. I seen the askar 103 could be reduced down to f 4 and wondered how it would be with chromatic aberration using only one element of ed glass.
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I have had quite good results with the 0.6x reducer and an aps-c dslr as you can assess in the link below. Yeah that's a great pic of Andromeda. I am using an ASI 294 MC pro. I should have mentioned in the original post that I am also getting really bad star shapes in the corners in additon to the chromatic abberation. I see some elongation in the corners of your picture but not as much as what I've gotten. See this image of the California nebula using the 0.6 reducer taken with duo band filter. https://www.astrobin.com/full/4xef9q/0/ |
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Perhaps slightly increasing the back focus would improve the elongation of the corner stars. I would probably try adding a millimeter to see what happens.
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Have the same scope with the reducers and have no problems at all, with camera 533 MM
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Have the same scope with the reducers and have no problems at all, with camera 533 MM The sensor is smaller in this case, and it's square shape allows a "better use" of the field. Perhaps the best way to use the x0,6 reducer.
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I purchased the same items. Last week I installed the 0.6x reducer to test.
I was very disappointed with the stars, even halfway to the center of the field. I quickly removed it and reinstalled the 0.8x reducer to resume my nights shooting. I am afraid the 0.6x will be in its original box, sitting on the shelf.
I will say that I am very happy with the 0.8x reducer. It does a great job.
Don I am unable to edit the previous post. Update: I added the Askar back focus adjuster which gives 2mm of adjustment. After some tweaking, I am getting much better results with the 0.6x reducer and can now recommend it using the ASI 2600MC Pro. Don
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I purchased the same items. Last week I installed the 0.6x reducer to test.
I was very disappointed with the stars, even halfway to the center of the field. I quickly removed it and reinstalled the 0.8x reducer to resume my nights shooting. I am afraid the 0.6x will be in its original box, sitting on the shelf.
I will say that I am very happy with the 0.8x reducer. It does a great job.
Don
I am unable to edit the previous post.
Update:
I added the Askar back focus adjuster which gives 2mm of adjustment. After some tweaking, I am getting much better results with the 0.6x reducer and can now recommend it using the ASI 2600MC Pro.
Don
Very interesting. Could you provide an image ?
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Very interesting.
Could you provide an image ?
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I purchased the same items. Last week I installed the 0.6x reducer to test.
I was very disappointed with the stars, even halfway to the center of the field. I quickly removed it and reinstalled the 0.8x reducer to resume my nights shooting. I am afraid the 0.6x will be in its original box, sitting on the shelf.
I will say that I am very happy with the 0.8x reducer. It does a great job.
Don
I am unable to edit the previous post.
Update:
I added the Askar back focus adjuster which gives 2mm of adjustment. After some tweaking, I am getting much better results with the 0.6x reducer and can now recommend it using the ASI 2600MC Pro.
Don
**I can now say that I have gotten better results with the 0.6x reducer when using some spacer rings. I added into two 1mm spacer rings to my imaging train to increase by backfocus to 57 mm instead of the standard 55 mm. With any of my 2 mm filters it becomes more like 57.67 mm. Thank you to @Jon Bryan for suggesting that idea. The star shapes are still not perfect but certainly a lot better than when my imaging train was the standard 55 mm. That askar back focus adjuster you got would probably make it easier to dial in the backfocus perfectly.
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Very interesting.
Could you provide an image ?
Here are links to my google drive with samples. There was some minor vignetting, but the flats took care of it.
I will take down these links in a couple days. Hope this helps. Let me know after you get them so I can close the link.
There is no cropping on any of these images. I may dial the back focus adjuster out a tiny bit more to see if I can get any improvement.
Don
https://drive.google.com/file/d/1FHRDE7V4RbKMJIwfnyrukMX678xstxzM/view?usp=sharing, https://drive.google.com/file/d/1aB1lTUM7Ii9NoWxCqXBTPWZ8pLNJag_-/view?usp=sharing, https://drive.google.com/file/d/1afh6ug8T3yCo0qcRqMiL6pvA4bHEV4Dg/view?usp=sharing
Thank you ! Stars are not perfect in the corners in these images, but the sensor is quite large for such a reduction factor. I hope you will find the correct distance.
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If anyone is interested in selling theirs I am interested.
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No not me, very happy with this scope
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I found exactly the same issue with the 0.6 reducer. Using an Astronomik UV/IR filter although star shapes were great across the full field, blue stars across the field suffered from horrendous chromatic aberration. I didn't see the issue when using an L-Enhance filter
I've since bought the Askar Backfocus Adjuster and managed to dial in the correct back-focus, but not had chance to test again using the UV/IR filter.
Based upon your results, I'm looking forward to testing and hopefully achieving better results using the 0.6 reducer.
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the 0.6x reducer is fantastic if you're using a mono camera with narrowband filters... If you're using a colour camera, or a mono camera with LRGB filters, you're likely to see a lot of blue fringing in your final images...
Its one of those things - no such thing as a free lunch... You can't expect to pull a 700mm focal length, f/6.8 refractor back to 400mm f/4 and there not be SOME sacrifice in quality.
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