BORG 55FL F3.6 and 90FL F4

I think now it’s the time to publicly show up my 1st test result of last new moon weekend. Following both were taken by 55FL with 0.8x dedicated dedicated reducer (1st prototype) and SONY A7(no filter) and IDAS HEUIBII filter.

casper2This is one of my most favorite targets and I always wanted to cover both clusters and nebulae in one frame. This scope allowed me to do that. Probably Sh2-240 should be perfect target in its size and the speed of this optics next time. auriga1

I didn’t expect left faint nebulosity (Sh2-235?). So I should re-try in slightly different framing next. Also Auriga was still too low angle. So the left side of image was affected by light pollution.

These two images remind me of medium format film era at viewpoint of the field of view and resolution. I’m feeling these are something similar to 6×7/6×9 film format with BORG 350mm or 400mm scopes I was using that time. But I believe these images’ resolution should be better.

Newly-designed super reducer for 55FL looks superb. Although I feel we might need some tweaking for better performance, overall it was what I expected. The field of view by 200 mm focal length and full frame sensor – this was what personally I was eager for. There are other 200 mm telephoto lenses in the market. But these results assured me of telescope-like clean, high contrast and sharp images as expected.

Also there is the one thing I want to clarify. I’ve never adjusted the color balance in these images. HEUIBII filter did great job. I highly recommend HEUIBII to the modified camera owners if the sky is dark enough. As shown in Auriga, if the sky is light polluted, LPS-D1 or LPS-V4 do better job. But as long as the sky is dark enough, HEUIBII is the best for modified DSLRs. Keep in mind, HEUIBII works for regular daytime shots too as described here before. Search with HEUIBII at my blog. You can see some my test results.

I applied the flat. But I wonder how much different between with the flat and without. Very even illumination entire full frame sensor. Even if no flat taken by some reasons, we don’t have to be disappointed at all. Still flat enough. I took more pictures. I will add them here later on.

Following picture is taken by one of very serious BORG users – Kok Chen with his 90FL F4 and modified A7S.  His location is not astronomy favor in weather wise. But he is always doing his best efforts to shoot day and night.

scaled25-8bitsHere is the comment from him.

Optical train is 90FL and 7872 flattener, filtered with the IDAS LPS-D1 to a Hutech modified A7S.
The skies here are very bright and the LPS-D1 is noticeably better than the HEUIB for NGC7000.

The A7S has quite low read noise, so I took 97 frames (I threw one frame away because the FWHM was higher than the others) at 30 seconds each,
ISO 2000. I did not have to auto-guide the Takahashi EM-11 because the exposure times are so short. Stacking is aligned with Nebulosity 3.
And processing is done with a combination of Nebulosity 3 and Photoshop.

Dark frames are taken as usual, but the flat frames (with bias removed) are taken with a white JPEG from an iPad 2 that is
about 1″ from the front of the 90FL objective.

The original short dimension (2848 pixels) of the A7S frame is cropped by 100 pixels,
and the width is cropped so the result is a square (the above image is rotated 90 degrees from original frame).
The combination is wide enough to include both NGC5000 and the Pelican are both in the frame.
The JPEG above is scale down by a factor of 4 from the original crop.

I look forward to his next image soon.


~ by tedishikawa on August 26, 2015.

5 Responses to “BORG 55FL F3.6 and 90FL F4”

  1. Hi Ted,

    Very nice! Beautiful images.


  2. Thanks, Fred
    I like the scope very much!!

  3. Ted, is it possible for you to provide full resolution images?

  4. Beautiful! How long was your exposure, and how many subs? Were these calibrated with darks?

  5. Wonderful work Ted.

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