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LP filter for F/1.2 optics
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Joseph Rome
I have the L-eNhance which gives fits to processing anyone with knowledge of a good 2" filter for an optical system of f/1.2 please let me know. Joe Rome |
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Blair MacDonald
What processing issues is the filter causing Joe? F/1.2 is a bit much for most interference filters. Blair (www.nightanddayastrophotography.com) -------- Original message -------- From: Joseph Rome <romejoseph9@...> Date: 2021-11-29 10:33 p.m. (GMT-04:00) To: ImagesPlus@groups.io, Info@..., "fastar-hyperstar@groups.io Group Moderators" <fastar-hyperstar@groups.io> Subject: [ImagesPlus] LP filter for F/1.2 optics I have the L-eNhance which gives fits to processing anyone with knowledge of a good 2" filter for an optical system of f/1.2 please let me know.
Joe Rome |
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Joseph Rome
Hay Blair, Well the flats seem to be changed from frame to frame leaving the outer edges. I just responded to another group and a copy below. This is a little out of the fastar group, but for interest. For some time now I have been interested in doing constellations , and to cut things short the camera is the ASIZWO071MC ("C" sensor) attached to the guiding scope with (https://astronomy-imaging-camera.com/product/new-holder-ring-for-asi-cooled-cameras78mm-diameters) and a adapter for a camera lens with (https://astronomy-imaging-camera.com/product/eos-t2-%e2%85%a1-adapter-suitable-for-all-asi-cameras) . The reason for this reasoning is I had a Tamron 75-300 lens and wanted to try it out. The above was connected to the guiding scope by a rail clamp. Easy but this showed issues with flats preventing stitching of the frames. Check the images on Flickr https://www.flickr.com/photos/42637403@N06/51700067255/in/dateposted-public/ .Go back a few images and you will see the problem. My thinking was the camera lens, the Tamron lens was one of the first batch and I had it for many years now. So I bought a new Lens for testing from Amazon Amazon.com : Lightdow 85mm F1.8 Medium Telephoto Manual Focus Full Frame Portrait Lens for Canon EOS Rebel T8i T7i T7 T6 T3i T2i 4000D 2000D 1300D 850D 800D 600D 550D 90D 80D 77D 70D 50D 6D 5D etc : Electronics It was cheap with reasonable optics, good for testing. The optics on this was very good, giving the "C" sensor just over 17+ degrees views and a 27+ degree with a "D" sensor. This has me so impressed I will get this new version of the lens set that most experts compare it to some lens costing $3600+ US dollars. Amazon.com : Samyang SYXP85-C XP 85mm f/1.2 High Speed Lens for Canon EF with Built-in AE Chip, Black : Electronics which is the parent company to the lens I just bought. The problem is I am stuck in Austin, Texas without any means of transportation to a dark site, and with the filter I have I can get the nebullisity easily, but not well because of the "V" curve. I want to go further from the F/1.8 to the newer optics taking me to f/1.2. I have been doing this for a long time and have a reasonable belief that at a dark site you would have little issues doing frames that will blend together well enough to be very happy with this setup. I may have to go to a 72mm ($OUCH$) filter. Do you have any recommendations? Besides "Get real." Joe |
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John Schnupp
I could be way off base here but I think you might be fighting two issues with this.
First is the field curvature that is a result of very wide field of view short focal length lenses. It can be a challenge to stitch frames together when the filed curvature gets to be too large. You would probably do better to use a little longer focal length so that there is less curvature, the down side is that you would need to take more images to make the same mosaic. I've heard lots of good things about RegiStar being able to handle image registration when lots of other programs struggle, at $179 it is not a trivial amount, but if you are doing a lot of very wide FOV imaging it might be a worthwhile investment. Second is the shift in filter response for very fast optics. I recall reading about it some time ago, when I was looking at upgrading my ZWO filters to something better. I had to go googling for this one. Was not able to find the exact article/page I read then but the gist of it is that as the f/ ratio decreases, the light cone gets wider and wider. As the angle from perpendicular, θ, gets larger and larger the incoming light no longer passes thru the filter at the desired frequency, the frequency of light that does pass is shifted. I found a presentation that talks about this in a few slides, http://www.aicccd.com/archive/aic2007/Goldman-AIC2007Talk2.pdf, starting on slide 25, Blue Shift With Faster Optics. According to Optolong specs the bandwidth of Ha is 10nm and OIII is 24nm on the L-eNhance filter. My suspicion is this is probably what is happening here. Narrower bandwidth is not always desired or wanted in a narrowband filter. See slide 38, Conclusions (2) where they mention that "off the shelf" filters are good for f/ 3.5 and higher and that under f/ 3.5 need specialty shifted filters. John Schnupp, N3CNL
2007 R1200RT 67,550 (hibernation)
1995 XLH 1200 106,495 (retired)
Georgia, VT44.7675°N, 73.1592° |
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Joseph Rome
I thank you for that information. For testing tonight I set the F stop at 6 made flats and they look a little better so I will let people know what happened with this. Joe Rome I could be way off base here but I think you might be fighting two issues with this. |
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Demetry Millas
I hear the IDAS NBZ works well with fast scopes.. but @ f/1.2..not too sure... but much better than the Lextreme. On Mon, Nov 29, 2021, 9:33 PM Joseph Rome <romejoseph9@...> wrote:
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Joseph Rome
Thanks for the tip! But I have found out the L-eNhance does work, the focal length of the lens is an issue in the city's light pollution, and will work well at a dark site. Joe On Thu, Dec 16, 2021 at 8:11 PM Demetry Millas <demetrym@...> wrote:
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