16 replies to this topic

[fate187]

Warning: DPAC infestation is spreading in the refractor forum on CN. Blanks and flat mirrors are sold out world wide due to peoples believe, that this is there cure

 

I recently aquired a TEC160FL from a kind seller from whom I already bought a Tak FC100DC and the AOM160 f/10. I am exchanging major scopes from my collection and the TEC140ED had to go for this FL lens. And since DPAC testing seems to be the best diversion during bad weather this beautiful 160 fluorite lens fits right in now.

BTW: This very night I will have to change to test it under the sky.

 

After all the recent threads in this forum on DPACing refractors I re-build my set up. I already had ronchi screens (66, 133 and 200lpi) for some time and now got a 3D printing ronchi screen/LED holder, that nicely fits into the 2" focuser extension. Additionally, I got LEDs in white, red (617nm), organge (600nm?), yellow-green (568nm), green (252nm) and blue (465nm).

Compared to my older tests (on the Tak100, TEC140, CFF185, etc) where I used my iPhone to take pictures, I now employ an Canon 500D/Rebel T1i and a Canon 50mm 1:1.8 lens. In a discussion with Peleuba, Jeff B, Scott in NC and the former owner of the telescope Donadani I learnt quite a lot on "proper" testing technique and methodology. DPAC testing can be a quick way to look at a lens, but if you are careful there is a lot information that you can scrutinize from it!

 

How I tested: I use an 200lpi ronchi screen. Be advised that the higher your lpi the more severe the results may look. I used a white light LED and color balanced my camera in order to match the respective channels. Shutter times were very short ~ 1/2000s, due the light intesity. ISO was at 100 for white light and 200 for the colored LED. I used Pixinsight for cropping and channel extraction into RGB. However, because the extracted channels are only greyscale (is there another solution?), I also employed an online site to split the channels. This gives them their respective color - nice for viewing. But the grey scale channels give more contrast imho.  I also tested with the other color LEDs and they are included in this test in the following posts, but there is not much additional information to be found there. Null images were tuned in order to give best contrast on surface features. I think this is important to point out, as one can easily shift the grating and make to lens look smooth .

 

Top row is always inside, mid row outside focus, bottom row is Null image. First image montage is colored RGB split channels, second montage is grey scale RGB split channels.

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[fate187]

Separate test with the color LEDs. Not perfect when it comes to illumination. However, I personally think the Null images look a little bit better - meaning more contrast.

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[Scott in NC]

This is very nice!  And by that I mean not only that you have a very nice scope, but that you did a wonderful job both with your testing procedure and with presenting the images here.  Now let’s hear your interpretation of the results. 

[Scott in NC]

I need to figure out how to present my images the way that you and Jeff do.  My current method takes up several CN posts and makes it more difficult to directly compare all the images without having to scroll up and down the screen.  I like that you can see all of your images at one glance, which I think makes it easier to interpret them.

[fate187]

Test set up and the beautiful lens. This is lens assembly astetically very pleasing - not a single dusk flake or surface features visible, perfection?

 

Now the DPAC test shows essentially perfect straight lines in red and almost in green - slight overcorrection there. In blue there is more spherochromatism visible manifesting itself in the bending of the lines. However, only a very small focal shift of the colors, which is visible from the red and blue channels (inside/outside focus). Pay attention to bars that are almost not visible towards the edge of the lens. Their similare visibility depics almost no focal shift of the colors red to blue.

 

For the surface features lets look at the Null image done with green 525nm LED:

There is zone visible starting at ~48mm radius (60%) going almost to the edge to 73mm (91%). This zone covers about 47% of the lens area. The features almost disappear in yellow-green to orange/red light LED. I think this zone is very shallow. I am looking forward to tonights star test to see if it will be visible. I only remember my LZOS130 f/9.2 having a small center zone which I was also able to see during star testing.

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Edited by fate187, 09 April 2023 - 08:46 AM.

[fate187]

I need to figure out how to present my images the way that you and Jeff do.  My current method takes up several CN posts and makes it more difficult to directly compare all the images without having to scroll up and down the screen.  I like that you can see all of your images at one glance, which I think makes it easier to interpret them.

Scott, In Pixinsight you can put the images to your liking. I also like using Irfanview which is a very light free (like in free - no costs, no ads) image viewer for all formats. It also lets you do the basic things like resize, saving to various formats - also RGB extraction. I then just open multiple windows each with the respective color and foci side and place them on the windows desktop. Use the Windows Snipping tool to acquire what you want the whole image montage and you are done

Edited by fate187, 09 April 2023 - 08:52 AM.

[fate187]

Outfitted for (personal) first light

 

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[Jeff B]

Outfitted for (personal) first light

And....?

[fate187]

Garbage scope, did you expect anything else?

 

No no no...! Fitted with Binoviewer, 2.6x Baader GPC and 9mm Delites planet Mars was very beautiful! Still small (5" I think) it easily showed polar caps and features on the planetary disc. I am not familiar with Mars and its features so I can't name them. But the view was extremely pleasing. The seeing was abviously playing along nicely.

I hunted some double/triple star systems down to 0.9" in Leo, Cancer and Gemini. The most difficult system was HD55130 a nice double with mag 7.2/7.3 and < 1.0". And there was this other nice triple system "Tegmine" in Cancer...

 

On to some star tests with the binoviewer and 2.6xGPC on Pollux showed very well in- and outside views. I may be inclined to say that it is the most symmetric star test I have seen. But I haven't done star tests for some time. In mono view with 2mm Vixen HR the view was similarely pleasing.

 

At first I had doubts of the combination with bino and 2.6x GPC. The later I have to use, because I am using the Gutekunst ADC. That piece eats up additional light path. My doubts were put to rest .

[donadani]

Great to read you´re fully satisfied - not that I had any doubts about it... but nevertheless - nice to read

 

Wish you much fun with that nice g&g scope - think you will miss your 140 not too much anymore

 

After many - that´s really THE goldilocks scope for me! 

 

cs

Chris

[fate187]

I just need the handle, but you are correct, the added weight is not much of an issue. Thanks

 

edit: I also observed Venus shortly and I was equally impressed by the absence of color. I am looking forward to the next moon phases and I want to compare it to the CFF185.

Edited by fate187, 10 April 2023 - 03:27 AM.

[visual-companion]

Great to read you´re fully satisfied - not that I had any doubts about it... but nevertheless - nice to read

Wish you much fun with that nice g&g scope - think you will miss your 140 not too much anymore

After many - that´s really THE goldilocks scope for me!

cs
Chris

Adverse fate for APO140ED #736! The first and second owner sold it to finance an APO160FL.

[fate187]

True Marcus .

Final DPAC test on the TEC160FL with 6x7 TEC flattener. I am directly comparing inside/outside/null images to the image sequences without flattener. Top row is with, bottom row without flattener. I having difficulties to see much difference there. Maybe in red/green are tiny bit more undercorrected? I see less focal shift of the colors from red to blue with the flattener. Also Null images are very difficult to judge, because of the sensitivity of the test. A small shift of the grating or even touching the focuser will give ever so slightly different contrast features of the lens. However, I tried my best to show the "worst".

 

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[Weisswurst Josef]

Adverse fate for APO140ED #736! The first and second owner sold it to finance an APO160FL.

Skipped the TEC 140. Moved directly to TEC 160 ED #045/2010.
Bought from first owner. No, will not sell FS-128 for that ...

 

Grüße aus der Münchner Schotterebene,

Andreas

 

 

PS

No I`ll not DPAC it. Although this seems to be the new religion.

Nether with an expensive mirror, nor with pricy motor-waste-oil.

Although I love the smell of later.

However with great interest I read the diverse test results. Good thing.

 

PPS

Had forgotten a picture from the lens. Sorry.

 

Edited by Weisswurst Josef, 10 April 2023 - 02:41 PM.

[Alan S]

I just need the handle, but you are correct, the added weight is not much of an issue. Thanks

 

edit: I also observed Venus shortly and I was equally impressed by the absence of color. I am looking forward to the next moon phases and I want to compare it to the CFF185.

I also have a TEC160 FL (from 2011) that I acquired by parting with an excellent TEC140….and last night I observed Venus at 373x using a Televue 3mm Delite just after sunset. Seeing was excellent.  I too am still amazed at the color free images the telescope produces.

 

Alan

Edited by Alan S, 10 April 2023 - 09:51 AM.

[fate187]

I would like to add one more image montage comparing Null images with 66lpi vs 200lpi and in doing so explaining some learnings I made in the process.

While a higher line density is more sensitive for inside/outside focal plane DPAC tests, at least for my set up I get sharper images using a lower lpi grating. In my images of DPAC there were always multiple images superpositioning while being slightly shifted to each other giving an unsharp image especially for Null.

 

With the lower lpi there are not necessarily less images superpositioning, but the spacing is smaller yielding an overall sharper image. The attached image shows top and middle row with 66lpi. They are virtually showing the same features, the emphasize is just different. Bottom row is with 200lpi. However, the contrast or grating is physically easier to tune with higher line grating.

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[NevelP]

Adverse fate for APO140ED #736! The first and second owner sold it to finance an APO160FL.

Adverse fate again, though not for me, as I now own this scope. I bought it a week ago from the guy you sold it to, marcus, who has not looked through it. I'm hoping for many clear nights with it. I'll test it tomorrow.