Using "Astrophotography Lab" to Determine Optimum Exposure Time

[STEVE333]

Thanks for putting this out there, Steve. I finally got the chance to run through the process with the Iris data I collected in September. The graph showed I am well past the knee of the curve with my 180 seconds subs. The recommended exposure settings didn't change the exposure time, but raised the ISO setting to 1600 (from the 800 I am using now). I will have to sit down and figure out what this all means now

Bob

You're welcome Bob.

I don't know much about the "Recommended" settings analysis from the program. For my system it recommended ISO = 1600 and Exposure Time = 180 sec. The Recommended settings yielded almost identical Stack SNR, so, no improvement there, but, it would have lowered the Dynamic Range by 0.5 Stop. Because of my 1 min "Unavoidable delay" the much larger number of images (shorter exposure time) would have caused a lot of lost imaging time. The Recommended settings may work for some individuals, but, they didn't work for me.

Just my opinion.

Cheers,
Steve

[JayTee]

Hi Steve,

Don't forget there's a flip side to the dynamic range portion of the exposure time equation. If you have to throw away a 5 minute exposure in essence that equates to throwing away two 3 minute exposures. Although your delay time is greater because of more images you will save time if your system is such that you routinely throw away subs. Throwing away a 3 minute sub is not as painful as throwing away a five or six minute sub. Or put another way, every minute past 3 minutes is a chance for something baaad to happen! :sigh:

Cheers,
JT

[STEVE333]

Hi Steve,

Don't forget there's a flip side to the dynamic range portion of the exposure time equation. If you have to throw away a 5 minute exposure in essence that equates to throwing away two 3 minute exposures. Although your delay time is greater because of more images you will save time if your system is such that you routinely throw away subs. Throwing away a 3 minute sub is not as painful as throwing away a five or six minute sub. Or put another way, every minute past 3 minutes is a chance for something baaad to happen! :sigh:

Cheers,
JT

Looks like my laptop wireless internet has just gone out! I'm connected to the router with an Ethernet cable for now. Bother!!!

Sounds like you have some guiding problems JT. Sorry to hear that.

Since I've gotten the CEM40 EC I haven't had to throw away a single frame even though they are all 9 min subs. I do get lots of airplane trails (and a few satellite trails) because I'm in the flight path for airplanes landing at the San Jose Airport. They are about a mile up, but, show up very bright in the subs. However, the ImageIntegration process (final step in stacking the images) in Pixinsight removes them nicely. The image below is the rejection map (the pixels rejected from contributing to the final stack) from Integration. There were 5 frames out of 52 that were affected causing all the trails seen below. None of these show up in the final stacked image! All 5 of the "bad" subs were included in the stacked images.



Cheers,
Steve

[JayTee]

Since I've gotten the CEM40 EC I haven't had to throw away a single frame even though they are all 9 min subs.

WOW, I wish I could say that. But my post is just as much for others who, like me, wind up throwing away at least 25% of their subs. The current condition of my AVX mount is, let's just say, not stellar.

Next month I will be ordering my CEM60 so hopefully I can join the club you're in.

Cheers,
JT

[STEVE333]

Since I've gotten the CEM40 EC I haven't had to throw away a single frame even though they are all 9 min subs.

WOW, I wish I could say that. But my post is just as much for others who, like me, wind up throwing away at least 25% of their subs. The current condition of my AVX mount is, let's just say, not stellar.

Next month I will be ordering my CEM60 so hopefully I can join the club you're in.

Cheers,
JT

Congratulations! It should solve your guiding problems.

Enjoy,
Steve

[bobharmony]

Sorry you are having so much trouble with the AVX, JT. Since I tweaked the gear mesh for DEC and RA on the ASGT, I toss about 1 sub in 25 (knocks wood).

Steve, I am leery of the ISO 1600 recommendation as well, I noted that it would lose more than a stop of dynamic range. I am satisfied that where I am (180 seconds at ISO 800) is a good place for me right now. If I ever get a triad or quad filter, I would consider going longer, but for now I am picking up and dealing with the LP, and collecting data as fast as I can. Every decision is a trade-off, there is no right or wrong method, just figuring out what works for you. Impressive rejection on your plane trails. I don't get nearly as many as that, but Kappa-Sigma stacking with DSS is just as effective at taking out the few that do creep in.

My dream mount would be the CEM60, but that won't be happening anytime soon, so for now, I will keep on keepin' on.

Bob