89 replies to this topic

[Jeff B]

Pre Starfire too.  

 

This is the trailer for the film soon to be released.

 

Jeff

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[Scott in NC]

So this looks to be oil-spaced and out of collimation, correct?  

[garret]

Looks like a 'b' movie...

Edited by garret, 07 April 2023 - 12:17 PM.

[Jeff B]

Just the objective lens and a focuser with a backplate were shipped to me.  These mid 1980's vintage AP scopes used a 7" O.D. tube which is identical to the Hastings 7" O.D. tube used today by many for their ATM projects, including mine.  A. Jaegers sized their 6" achromat lens cells to use this type of tubing as well.  Indeed, while Roland produced complete OTAs, he, at the time, sold this objective as a drop in replacement for the very popular Jaegers 6" F8 achromatic objective, right down to the cell's bolt pattern.  It was plug and play replacement. 

 

And that's exactly what I did as I have an old bino-friendly OTA that I put together sometime ago around a vintage Jaegers 6" F8 objective, D&G backplate (D&G used Hastings tubing as well), and a nice AP 2.7" focuser with the FT option.   

 

The Jaegers objective departed some years ago but the OTA remained so.......

 

It all fit together perfectly with no tweaking of the focuser/backplate alignment, or that of the objective, as you can see in the above images.  For you ATMers out there, just how often does that happen?

 

I placed OTA in DPAC, let it sit overnight and ran off the usual images.

 

FYI, Vladimir Sacek gives an estimate, and a brief discussion, on his most excellent website as to this lens design as example number 8:

 

https://www.telescop...po_examples.htm

 

Roland has told me on a couple of occasions that these older lenses were designed for visual use with best correction in yellow, though a hand full were corrected for the film of the time but I'm not sure what part of the spectrum that is.  He also said these were similar in secondary spectrum (color focus) to an achromat with 3x to 4x the focal ratio, so for this vintage AP objective, that would be F24 to F32, certainly not too shabby at all for visual use.

 

First, the white light "Master Images".

 

Jeff

 

 

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[Jeff B]

Now, the usual inside and outside of focus color montage images derived from isolating and blending the individual red, green and blue color channels from the digital white light images

 

 

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[Jeff B]

Now the at focus image in green light with the contrast enhanced to highlite figure details.

 

It's late and I'll post some of my comments tomorrow but please feel free to add yours as well.

 

Jeff

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Edited by Jeff B, 07 April 2023 - 11:02 PM.

[Scott in NC]

I see over correction in all colors, with best correction possibly in red, and worst correction in blue. The white light testing shows quite a bit of CA, as expected with a pre-ED scope.  The at-focus image shows a reasonably shallow zone near the center.  The lens appears to be pretty smooth.

 

This has a bit more SA than I’d want to see on an A-P scope, but suppose that’s not entirely usual if it was created in the days before A-P used an interferometer for testing while figuring.

 

Nice job, Jeff!

[Jeff B]

Thanks Scott and my take is quite similar on this older objective...best correction in red and overcorrected everywhere else with the blue also out of focus relative to  green through red (secondary spectrum).

 

It's interesting to me to compare the white light images of this sample to those of my old AP 178F9 pre-ED Starfire as you see in the attached inside of focus shots.  There are similarities, for example, both are overall overcorrected with the 178 less so.  Both show a "miss" in the blue focus relative to green through red.  Both show a subtle green fringe on the inside edges of the outer line shadows.  But, notice the difference in fringing on the outside edges of the outer shadows.  The 6" F8 has a pink/purple tint to those fringes, while the fringes on the 178 are mostly blue.  Finally the 6" F8 has a subtle ruddy border to the center shadow, the 178 does not.  This difference in color balance is noticeable at the eyepiece too, and more on that later. 

 

Panning through focus, I saw no signs of astigmatism (center line clocking/rotating).  

 

Looking closer at the shape and flow of the line shadows, I see the center "zone", which covers ~40% of the aperture, is actually rather neutral. So I guess I could better define the "zone" as an outer zone bending towards overcorrection past the 40% span.    I see the same thing in the in-focus green image.  The center is evenly illuminated, the outer 60% of  span is not, indicating a figuring error out there.   This all pretty much goes away in red (but it is still very slightly overcorrected overall).

 

I find it interesting comparing these images from an almost 40 year old objective to those published by Paul for the SV180.

 

And, of course, there is that edge thing....

 

Jeff

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Edited by Jeff B, 08 April 2023 - 10:27 AM.

[Scott in NC]

Jeff, explain the significance of the two red laser points seen in one of your pictures in post #1.  I thought that was showing miscollimation (or likely axial misalignment of the focuser or the lens cell to the tube), but maybe not since you didn’t mention it.

[Jeff B]

Jeff, explain the significance of the two red laser points seen in one of your pictures in post #1.  I thought that was showing miscollimation (or likely axial misalignment of the focuser or the lens cell to the tube), but maybe not since you didn’t mention it.

Sure Scott, that photo was taken with me standing behind the scope which is pointed at the DPAC flat.  That second red dot off to the side is the reflection of the laser beam exiting through the mask center hole and off of the flat.  I will shamelessly say I'm pretty good at refractor ATMing.   The Cheshire image is slightly off due to a subtle camera angle while visually, the dot was very close to the cheshire aperture.  Oiled triplets only have two surfaces that can reflect light from the cheshire.

 

Jeff

[Jeff B]

That turned edge is real and about two, maybe three, mm wide.  Attached are shots taken with a nice 140mm mask.  A 145mm mask probably would have hid the edge but I had the 140mm mask at hand.

 

Jeff

 

 

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[dec12252]

Reading through this thread motivated me to DPAC test my (circa 1998) f/6 AP130EDF scope.  I took Ronchigrams using a white light LED as well as separate red, green, and blue LEDs.  Below are the inside (top) and outside (bottom) focus Ronchigrams with RGB extracted from the single White light LED Ronchigrams (borrowing Jeff B's technique). Ronchigrams taken with the separate colored LEDs showed the same result.

 

The lens is well corrected in red and green and slightly overcorrected in blue. I have not analyzed these Ronchigrams using Maciej's AOS yet.

 

When I get around to it I will also test my f/7 AP155EDF.

 

Dave

 

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[Scott in NC]

That’s very nice, Dave.  What processing software do you use for separating white light into R, G, and B channels?  I know that Jeff B. uses an old version of Paint Shop Pro, but I’m looking for something inexpensive that will work on my MacBook.

[Maciek_Cz]

Dave, very nice telescope!

Scott, you can use Gimp for this job.

[Scott in NC]

Thanks for the advice, Maciek.  Years ago I used to use GIMP on my previous Windows PCs, but it’s good to know that it will work on a Mac too.  I’ll give that a try.

[dec12252]

I separated out the RGB channels using Pixinsight on a Macbook Pro.

 

I plan to keep this scope for a while

[Scott in NC]

Sorry to take your thread off on a tangent Jeff, but I just wanted to report that I loaded GIMP onto my MacBook, and am amazed at how easy it is to use to separate out the R, G, B channels.

 

Jeff (or anyone else who's knowledgeable about this), do you think that just shooting in white light and breaking out the channels via image processing is truly an adequate substitute for performing DPAC testing 4 times for each scope in white, then R, G, and B?  If so, I'll just shoot in white from now on, as this will be a great time saver.

[Maciek_Cz]

Scott, the problem with this approach is that you don't know the wavelength. You only know what color it is.

In the qualitative approach, this is enough, in the quantitative one, for example, for the AOS analysis,

I think it is also enough, because we make a greater error in the selection of parameters

and the assessment of the similarity of ronchigrams than with a 10-20nm error in the wavelength.

[Scott in NC]

Thanks for the advice.  I'll experiment with more testing using individual LEDs and seeing if the results differ from white light only and then separating into RGB.  And if I don't see any differences after extensive testing, then I'll convert to Jeff's method for all future testing.

[Jeff B]

Scott, it took me a while to really latch on to and get great results from using a single white LED and then splitting and blending the RGB channels.  There is a  whole lot of useful information in such shots as there are actually 3 small LEDs being used (red, green and blue) and they are all at essentially the same physical distance from the lens center.  It's sooooo much easier and if you choose a "warmer" white light LED, along with the proper white balance settings with your camera, blooming in the red and blue is basically eliminated.  I still use a single green LED for my at focus images as it's much easier for me to achieve a good at focus image with a single color. In my case, my choice is green. 

 

Recently I reshot DPAC images with my wicked excellent TEC 160ED as it was already on the bench being used for indoor star testing.  I specifically made back to back comparisons with a single green LED and the white light LED with the green channel singled out.  This was more of a test for process creep.  I had gotten excellent matches between the two techniques before and I wanted to see if I got the same result now.  I did and the result is attached.    Any differences you may see are exposure related.

 

And speaking of exposure, it matters to get good quality images.  The attached comparison, in green with the single green LED, shows, from left to right, 1/50, 1/125 and 1/200  second exposures, all at ISO 50.  The blooming at 1/50 second is easy to see and it reduces the contrasts of the line shadows.

 

Keep experimenting to see what's best for you....and that may change overtime as your data capture and processing evolves.

 

I'll be posting DPAC simulations next

 

Jeff  

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[Scott in NC]

Thanks, Jeff.  Right now I only have two Ronchi eyepieces, one with a single green LED, and the other with white, red, and blue LEDs all together in the same eyepiece.  In theory that should work well, but the problem is that the red and blue LEDs are off-center.  They're close enough to the center that the eyepiece works well when used visually, but far enough off center that it's not possible to get my camera lens close enough without vignetting.  That's why many of my red and blue Ronchigrams look oblong rather than circular.

 

So I either need to just shoot in green and white and then split out the color channels, or else one day get 4 separate Ronchi eyepieces, each with their own single color LEDs.  If the former will provide the same data then I'd prefer to go that route.

[Jeff B]

Keep at it my friend.   "The more you work it, the more it works and the more it works, the more you can work it."

[David Lim]

I will add my DPAC image of AP 130 f6 as well here.   I used Adobe Photoshop to separate red, green, and blue channels from my white LED images.  The blue channel has moderate spherical overcorrection.   Red and Green are both well corrected.   Knife edge shows smooth figure with minimal zones.  My ronchi screen has 138 lines per inch.

 

 

 

Knife edge using green LED

 

 

 

 

[Jeff B]

Great work David and I love the KE image image.

[Scott in NC]

David, is that a true knife edge, or a single Ronchi grating line serving as a knife edge? I’m asking because I’d really like to be able to get pictures as sharp as that for my “at focus” images.