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Sky-Watcher 100mm APO + Apex-L + ASI2600MC Pro First Impressions

astrophotography equipment optics
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#26 Xentex

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Posted 19 December 2020 - 08:14 PM

I don't understand this based on what I have seen.  Starizona even says it only delivers a 30mm image circle.  I will have to try my 5DMKIV camera.

Just to be clear, I'm not using an Apex.  I was just commenting on the size of the Esprit 100's image circle, and that it's greater than 40mm.

 

The Esprit 100 documentation does say "40 mm" image circle in one place, and it says "full frame" in another.

 

My experience is the Esprit fully illuminates the ASI6200 sensor (43.3mm I believe) but I haven't found a backspacing where I can get clean stars in all four corners.  I'm attaching an example of what my corners generally look like.  (Single typical unprocessed H-alpha sub with auto-histogram.)

 

There's some vignetting at the corners, but it's only about 15% light falloff vs. the center.  The bigger issue is the star shapes as you approach the corners.

 

In any case, I'd expect the Apex-L (based on what Starizona says) to fully illuminate the ASI2600 with an Esprit 100, but the corners might not be pretty.

 

_2020_12_07_20_06_37_Ha_10_00_300_00s_0001_mosaic.jpg



#27 Jim Waters

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Posted 19 December 2020 - 08:27 PM

OK - thanks for the clarification.  I plan on using my Ha mod Canon 6D and stock 5DMkIV with the scope.  As for the Apex-L  "to fully illuminate the ASI2600 with an Esprit 100, but the corners might not be pretty."  That's the case.



#28 Xentex

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Posted 19 December 2020 - 08:45 PM

I'd like to see how good you can get your corners with the Esprit 100 and the full frame Canons.

 

I toyed with my spacing quite a bit and the image above is representative of where I ended up.  Adding further spacing seems to make the corners worse, and I can't bring it in any closer without having something custom built.  As I move further out the stars begin to radiate outward from the center, as you see in the upper left of the above.  Pulling it as close in as I can get they start to turn into "x" shapes as you see in the other three corners.  That seems to be as good as they get before they transition to being elongated tangential to the center.

 

I bought the scope to use with my ASI2600, and I'm pleased with it for that (APS-C), but I did want to see how well it can do full frame.  Pretty good for the price, I'd say, but needs some cropping.



#29 Churmey

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Posted 18 January 2021 - 05:02 PM

Just wanted to add that, when you add in a filter, you need to add in approx 2/3rd of a mm to your back focus - especially when using the apex, as it's tight tolerance should be within 1/2mm.  For example, if your using an optolong uv/ir filter, the backfocus then needs to become approx 58.6mm (as noted on the last page of the Apex instruction guide).  This will not help with the Vignetting but it will get you closer to the optimal backfocus distance. Without compensating for this, you would be outside of the optimal backfocus distance/tolerance when your at the standard 58mm.


Edited by Churmey, 18 January 2021 - 05:05 PM.

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