Nikon D5300 settings for AP

[pmwolsley]

Hi all...this is my first post on this site...

I have an Ha modded D5300 which I use with my Celestron 8" EdgeHD primarily at F10. On occasion I will also use my Celestron F7 FR. My journey in AP has always been to go deeper and deeper. I now feel that my ultimate goal is to image dust clouds around Nebulae. The Iris Nebula is my test DSO with all of its dust clouds that surround it. I believe that ISO200 is the "unity gain" setting for my D5300. This summer I concentrated on taking 500 second images at ISO200. At my dark site I found that 500 seconds just starts to saturate the brightest stars. The longest integration time I have tried is 4 hours. I am a summer AP enthusiast. My hands can't take the cold and I would be imaging from a big city. I always use BIAS, DARKs and FLATs. I use Startools exclusively and find that the dust clouds are always noisy and barely discernable above the sky background.

I want to figure out what my next step(s) should be...so here are a few questions.

-Is ISO200 the best ISO for my D5300? I believe that at ISO100 I would be throwing away photons instead of counting them. At higher ISOs I believe I am just giving up dynamic range and individual image exposure lengths.

-If 4 hours is not enuf integration time then how many hours is reasonable? Would attempting multi-night imaging pay dividens?

-Am I at the limits of my current imaging set-up?

I want to ponder these issues over the winter. I am trying to justify purchasing new imaging gear...possibly a cooled mono camera with filters. Alternatively, I could consider trading in my 8" EdgeHD for a bigger scope. I just want to be sure that there isn't something else I may have missed

Peter

[KathyNS]

Ideally, you want to run the camera at its "unity gain" setting. You are correct that using too low a gain (ISO) setting will lose precision, especially at low signal levels. Running at too high a setting will not gain any precision but will add noise. The unity gain setting varies for each camera. There are resources online that will tell you the setting for your camera.

Most DSLRs have a unity gain setting somewhere between 800 and 1600. So either 800 or 1600 (or something in between, if you've got it) will give good results.

[EDIT] Actually, it looks like unity gain for your camera is closer to 200. So you are probably as close to ideal as you can get.

[JayTee]

First off, I believe you are at a crossroads. To me you have taken your current equipment as far as you can reasonably go. The fact that your DSLR is modified and you're able to capture images to go all the way up to four hours of integration time says that you are well on your way to being a very experienced APer. So, I have some suggestions for you.

1) It's time for a new dedicated astrocam. A camera that is cooled so that the noise levels are essentially removed and is actually geared for astrophotography. It's time for a mono camera so that you can use filters. As a suggestion the ASI 1600MM Pro with filter wheel.
2) You need a different telescope, one that will allow you to take wide-field images like an 80 - 102 mm short focal length refractor. This will open up a whole new area of AP for you.

Just my thoughts,
JT

[pmwolsley]

Ideally, you want to run the camera at its "unity gain" setting. You are correct that using too low a gain (ISO) setting will lose precision, especially at low signal levels. Running at too high a setting will not gain any precision but will add noise. The unity gain setting varies for each camera. There are resources online that will tell you the setting for your camera.

Most DSLRs have a unity gain setting somewhere between 800 and 1600. So either 800 or 1600 (or something in between, if you've got it) will give good results.

[EDIT] Actually, it looks like unity gain for your camera is closer to 200. So you are probably as close to ideal as you can get.

Thanks Kathy for confirming the unity gain for my D5300 and confirming my thinking regarding optimum ISO. I had previously did some research and found that the read noise is lower at ISO 800 so I spend a summer shooting at that ISO. Last winter I realized that I needed to maximize the ratio of recorded photons to read noise so I dropped the ISO to 200 and used as long an exposure as I can achieve. The data is still challenging to develop so you begin to question your thinking.

Peter

[pmwolsley]

First off, I believe you are at a crossroads. To me you have taken your current equipment as far as you can reasonably go. The fact that your DSLR is modified and you're able to capture images to go all the way up to four hours of integration time says that you are well on your way to being a very experienced APer. So, I have some suggestions for you.

1) It's time for a new dedicated astrocam. A camera that is cooled so that the noise levels are essentially removed and is actually geared for astrophotography. It's time for a mono camera so that you can use filters. As a suggestion the ASI 1600MM Pro with filter wheel.
2) You need a different telescope, one that will allow you to take wide-field images like an 80 - 102 mm short focal length refractor. This will open up a whole new area of AP for you.

Just my thoughts,
JT

Thanks JT
Always great to be able to bounce ideas off of others APers. I should have mentioned that I also have an 80mm refractor which gives me fantastic images of the North American, Pelican and California Nebulae...to name a few. To be fair...I really like using the 80mm...just beautiful results. The 8" EdgeHD gives me tremendous challenges...which I enjoy. I am a retired Electrical Engineer with 30 yrs experience in real-time control systems. I also program in a language call LabVIEW. I have written lots of software for my Celestron CGEM and for image calibration so I love the nitty gritty.

Thanks for the recommendation for the ASI 1600MM Pro. I have been looking at the QHYCCD all-in-one cameras

Peter

[pmwolsley]

Another possible path for me could be to start using filters. My research has lead me to believe that using narrowband filters will also help push back the sky background away from the dust clouds. My gut feeling is that using narrowband filters with a DSLR suffers from always having to deal with the bayer matrix. The ISO would still stay at the "unity gain" ISO200 but the exposure times would get crazy large so as to collect enuf photons. The DARK signal might be correctable but the associated DARK noise might dominate causing me to lose any benefit from the narrowband filters. I define Dark Current as being composed of a DARK Signal and a DARK Noise.

Does my thought process make sense or am I missing something?

Peter