Curious if anyone has experience using this scope (or the 160) with a Canon DSLR, either an APS-C or full frame? If so, are there issues seen with the mirror shadow or shadow from any of the other construction around the sensor given the fast optics?
Takahashi Epsilon 130D with DSLR
Well written Engaging
Since no one answered this for hours, I will do.
I don't have an Epsilon 130D, but I had an Epsilon 180ED and I used it a lot. No matter you use APSC or FF, you will get lot of vignetting. However, a proper flat-fielding can handle it. You should not worry about it as long as you stick to the right calibration procedure.
I don't have an Epsilon 130D, but I had an Epsilon 180ED and I used it a lot. No matter you use APSC or FF, you will get lot of vignetting. However, a proper flat-fielding can handle it. You should not worry about it as long as you stick to the right calibration procedure.
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Wei-Hao and David-
Thank you for the responses.
Wei-Hao: since your D810A setup is probably closest to mine, I was wondering if I might ask you a question. How exactly are you taking your flats? My protocol is to use an LED panel dimmed to get an exposure time of 3 seconds while aiming for ~ 20,000 ADU as measured in SGP (16 bit). This has worked for me with other CMOS cameras. However, in the case of both my Canon 6D and (more surprisingly) my 7D Mark II which is APS-C, I'm finding that the flats do not properly correct the vignetting, particularly, in both cameras, from the mirror box.
Arun
Thank you for the responses.
Wei-Hao: since your D810A setup is probably closest to mine, I was wondering if I might ask you a question. How exactly are you taking your flats? My protocol is to use an LED panel dimmed to get an exposure time of 3 seconds while aiming for ~ 20,000 ADU as measured in SGP (16 bit). This has worked for me with other CMOS cameras. However, in the case of both my Canon 6D and (more surprisingly) my 7D Mark II which is APS-C, I'm finding that the flats do not properly correct the vignetting, particularly, in both cameras, from the mirror box.
Arun
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Hi Arun,
What you said somewhat surprises me. It should work. I sometimes use twilight sky for flats, sometimes use an LED panel. On the LED, I just try to keep exposures longer than 1/10 sec, to avoid flickering, and average about 30 of them. For the 30ish exposures, I rotate the LED panel to average out uneven illumination. I also point the camera to different parts of the sky for twilight flat, also to average out potential sky gradient. On my E180ED, I had used Canon 5D2 and Nikon D800/D810A. With this method, I never had problems. The mirror box vignetting is super obvious in the raw file, but it gets flattened out very nicely, pretty much all the time.
BTW, I always take darks (for light, not for flats) and biases, and I use the same ISO throughout.
Cheers,
Wei-Hao
What you said somewhat surprises me. It should work. I sometimes use twilight sky for flats, sometimes use an LED panel. On the LED, I just try to keep exposures longer than 1/10 sec, to avoid flickering, and average about 30 of them. For the 30ish exposures, I rotate the LED panel to average out uneven illumination. I also point the camera to different parts of the sky for twilight flat, also to average out potential sky gradient. On my E180ED, I had used Canon 5D2 and Nikon D800/D810A. With this method, I never had problems. The mirror box vignetting is super obvious in the raw file, but it gets flattened out very nicely, pretty much all the time.
BTW, I always take darks (for light, not for flats) and biases, and I use the same ISO throughout.
Cheers,
Wei-Hao
Helpful
Thanks, Wei-Hao. I will retake my flats a bit more carefully and rotate the panel to avoid issues of uneven lighting. Hopefully that takes care of it. The APS-C light frames and flats do seem fairly "normal" and seem like they should calibrate out.
Well written
Hello Wei-Hao - another question re the 130D/180ED. When imaging under very cold conditions (about 5 degrees F), I saw issues with triangular stars (pinched optics). My initial thought and based on an email exchange with another user was that the screws holding the primary in place were too tight. But talking to Takahashi North America, they suggested that the center knurled nut holding the secondary mirror in place may be too tight from when it was shipped. They suggested loosening it a little and also said that doing so would not ruin collimation. I found that a bit hard to believe given that the nut needs to be loosened to move the mirror back and forth and turn it. Has it been your experience that the nut can be loosened without ruining collimation assuming that the secondary mirror isn't directly touched? Thank you!
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Hello Arun
I own a Epsilon 130D. Your issue with stars may be due to constraints on primary. I had the same issue. You have to loosen the screws of primary to avoid astigmatism. The primary could move just a bit. If your primary can't translate a bit it is to stressed. CLS
I own a Epsilon 130D. Your issue with stars may be due to constraints on primary. I had the same issue. You have to loosen the screws of primary to avoid astigmatism. The primary could move just a bit. If your primary can't translate a bit it is to stressed. CLS
Thanks, @ManuManu. Looks like multiple data points indicate an overtight primary. I will check again when the weather is a bit warmer, and if there is still a problem, loosen the screws on the primary.
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