15 replies to this topic

[Joe G]

Here is another of my friend's scopes.  A Sharpstar 94 EDPH F5.5.  It is an air spaced triplet with two ED lenses.  I have not looked through this scope visually.  It seems very well made and has a nice focuser.  My green images missed focus a bit.

 

 

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[Joe G]

Green:

 

 

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[Joe G]

Red:

 

 

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[Joe G]

Blue:

 

 

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[Joe G]

White:

 

 

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Edited by Joe G, 16 April 2023 - 03:49 PM.

[Kitfox]

Is the huge difference between the strehl of the individual colors and the white because:

 

a) The differences between focal lengths for the individual colors manifests itself;

 

b) AOS isn’t designed for while light DPAC;

 

c) None of the above;

 

edit: or,

 

d) The white light AOS info is gone and my post makes zero sense!

Edited by Kitfox, 16 April 2023 - 04:10 PM.

[Joe G]

I noticed that too.   I dunno.   Need to ask Maciek.  There is a "white light" check box in AOS.  I am not sure what that means?

 

I would ignore the white Strehl calculation.  When I change the wavelength it changes the Strehl.

[CHASLX200]

Looks good.

[Maciek_Cz]

Hi guys, it doesn't make any sense to count Strehl for white light in AOS. This option is for visual purposes only. So that you can compare the simulation to black and white/grayscale photos.

[Joe G]

For clarity, I am going to delete the "white" AOS calculation above.

 

Thanks Maciek.

[Kitfox]

Hee hee, I edited my post above 

[Scott in NC]

Two comments:

 

1. I think I see a little more Ronchi band curvature in your actual images than in the simulated AOS Ronchigrams, so you might want to check that again.  It could just be an optical illusion on my part though.

 

2. It looks as if this scope is undercorrected in red, green, and blue, with the degree increasing as one progresses from red to blue.  I haven’t seen this a lot, but likely because most refractors are optimized in green, and as a result I’ve become used to seeing SA in red and blue in opposite directions (i.e., over/under).  I suppose this means that the null point is somewhere in the vicinity of red or maybe a little “left” off red.  Still, this isn’t anywhere near as bad as the now infamous SVX180.  Interestingly, I’ve heard some speculation that some of the imaging scopes with Chinese-sourced optics are intentionally nulled in red, as they really aren’t meant for visual use, and are meant to work with a focal reducer / field flattener which adds the opposite form of SA, therefore improving the undercorrection in green and blue.

[SandyHouTex]

They all look pretty straight to me, especially the green.  It doesn't look nulled in red.

[Cbaxter]

This looks to me like rather good optics overal. Unless I am missing something. I like my 94edph quite a lot. Though mine usually has the reducer flattener attached for imaging. For the price of these scopes and how fast they are at f5.5, well I've seen worse at a significantly higher price point.

[Foc]

Did your friend prefer not to use a reducer?  I have heard some reports that the dedicated EDPH reducer adds additional Chromatic error but I would have thought the flattening and focal speed characteristics make the flattener still worthwhile for imaging.

[Cbaxter]

Did your friend prefer not to use a reducer? I have heard some reports that the dedicated EDPH reducer adds additional Chromatic error but I would have thought the flattening and focal speed characteristics make the flattener still worthwhile for imaging.

The dedicated f4.4 reducer does induce some CA, unfortunately. The advertised spot diagram for the reducer accurately show the CA so it shouldn't be a surprise to anyone purchasing the reducer flattener. The 94EDPH itself at native f5.5, excellent visual views.