26 replies to this topic

[Joe G]

I was just learning this DPAC stuff when I did my original post about a week ago.  So after learning more I think it make sense to not add to that old thread and start a new thread which will be a better reference.

 

My scope is actually called a SW Quantum.  I guess that is how SW labeled the carbon fiber tube version of the Esprit.  It is the same lens.  It was supposed to be the premium version because of the carbon tube, but folks apparently are over obsessed with the coefficient of thermal expansion of aluminum being closer to glass.  So they stopped making the carbon fiber version and discounted them to get rid of them.  I have never noticed any material issues with the carbon tube and appreciate the weight savings.

 

As has been suggested by peleuba, I added a potentiometer to my setup to adjust the brightness of the LEDs.  The LEDs I used here are 2 volts bought off Amazon.

 

My Ronchi eyepiece is a 2" extension tube with a 2" square 100 LPI glass etched Ronchi screen taped to the top.  I butchered a 2" eyepiece cap to make the LED holder which I taped on top of the glass grating.

 

The flat I have been using is an old, somewhat scratched Edmund Optics 8" flat.

 

Also included here is an analysis using Maciek's AOS program to determine Strehl values, etc.

 

Here is a view of the lens tested and the scope.

 

 

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[Joe G]

So I will start with Green, well because I like green. 

 

Here is the inside and outside of focus fringes.

 

 

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[Joe G]

AOS inside of focus:

 

 

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[Joe G]

AOS outside of focus:

 

 

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[Joe G]

Red fringes:

 

 

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[Joe G]

AOS Inside:

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[Joe G]

AOS outside:

 

 

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[Joe G]

Blue fringes:

 

 

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[Joe G]

AOS Blue Inside:

 

 

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[Joe G]

AOS Blue outside:

 

 

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[Joe G]

And finally white fringes:

 

 

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[Joe G]

So if I did everything better it would appear the the Strehl ratios are as follows:

 

Green approx. 97

Red approx. 96

Blue approx. 90

 

So maybe not a bad polychromatic overall Strehl.  The scope puts up good views and one of the best star tests I have seen.

 

Not bad for a 150mm Chinese lens?

 

Thx.

 

Joe

[gstrumol]

The scope puts up good views and one of the best star tests I have seen.

You could have stopped there!   If it does all that why do you care about what 'numbers' it has or doesn't have?

 

Let me ask you this question: if you found out the number was 0.8 instead would what you see through the scope change? Or if it turned out to be 0.99?

 

(Beautiful images BTW)

 

Just enjoy it!!!  

[Scott in NC]

Very nice, Joe.  A week later it's like you're a pro at this!

[Scott in NC]

You could have stopped there!   If it does all that why do you care about what 'numbers' it has or doesn't have?

 

Let me ask you this question: if you found out the number was 0.8 instead would what you see through the scope change? Or if it turned out to be 0.99?

 

(Beautiful images BTW)

 

Just enjoy it!!!  

I can't speak for Joe, only for myself, but testing and measuring stuff like this really appeals to the geeky side that many of us have.

[Toddeo]

Some people sleep better after knowing they have a really nice scope !

[CHASLX200]

Looks good.

[Joe G]

You could have stopped there!   If it does all that why do you care about what 'numbers' it has or doesn't have?

 

Let me ask you this question: if you found out the number was 0.8 instead would what you see through the scope change? Or if it turned out to be 0.99?

 

(Beautiful images BTW)

 

Just enjoy it!!!  

Curiosity.  If it tested at 0.8 I would wonder what I was doing wrong.  If it tested at 0.99 I would think that there was a large marketing department behind the numbers. 

[Koop]

This whole Ronchi/DPAC trend has been an eyeopener and vicarious learninng experience for me. These results are convincing when the argument is made for the possibilities of achieving a quality lens cell from a volume Chinese maker. It's all about specification set in the original order, quality control, guarantees by the manufacturing plant and verification of quality standards by brand making the initial order.

[garret]

Good job!, another good telescope in the blue... I think SV can't take it anymore...

[Agatha]

According to what I have managed to learn about this testing, yours looks very good.  

 

I'm also very curious about your rings and the dovetail on top.  It's a color I've not seen before.  ..??

[Joe G]

Sad, but that used to be black.  Not sure what the deal with Chinese anodization is but it often fades to that color if exposed to the sun for too long.  The focuser on that scope is also faded.

 

It happens on many products.  My ZWO red cameras have faded. 

[Space_Race_T.J.]

At least it faded to a nice color IMO.

 

Do the red ZWO cameras start fading to pink? 

[Joe G]

Yes, or a pale red.

[Joe G]

Not to beat a dead horse.  I switched cameras to a Sigma FP mirrorless.  Much easier to use the screen to focus.  Images came out better.

 

So here are the new Ronchi images.  The at focus images appear much better.

 

 

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