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Exposure time and settings questions for newb - jonkjon - 2019-11-16

I am new to ST4 Imaging. I have been reading the manual, watching tutorial videos, as well as perusing the forums. I have also been browsing/practising with the software to get familiar with it. I have setup my imaging system, location, etc. During my trial practice runs, I am noticing that the exposure times, recommended in the Filters section of the Exposure Goals and Filters tab of the New Imaging Project section, seem to be unusually short. I know that it's hard for anyone to tell me specifically what I am missing as you would need much info about my system. However, I don't know where to begin as there is so much information to provide. I can generalize my imaging system and then perhaps this will narrow down what other info I need to gather.

I am currently imaging with an iOptron ZEQ25 CEM using a Skywatcher 80mm refractor with an .80x focal reducer. I use a QHY163M mono camera and mostly shoot LRGB with occasional Ha from a Bortle 4 sky site. I have used my own camera info as well as imported my camera information from the shared cameras. Gain/Offset is usually 50/35 for this camera when broadband.

With this setup, ST4 Imaging is showing exposure times of: Lum-180 sec, Red- 360 secs, Green-360 secs, Blue-240 sec.s (LRGB (Bin 1x1)) to obtain an SNR of 60 when exposing for Target Object/Main Extent. While I understand that ST4 Imaging is aimed at saving me skytime, this seems insanely short. I know I have to either be mis-interpreting what I am seeing or I have a setting wrong. Is this tab indeed telling me that all I need is a total of 19 mins. worth of integration? While I know the target is better suited for NB (I am still acquiring filters), and the scale is not ideal, I have exposed this target in the past (LRGB) for as much as 2 hours and still think it could stand another couple of hours. I have checked to make certain the correct information is displayed in the Target Selection (i.e. Imaging system, Location, Primary Focus/Focal Reducer, Auto Filter, Binning). I haven't had clear skies since purchasing ST4 Imaging so I haven't had a chance to test anything in terms of real world shooting.

I have attached some screen captures of some of my settings windows. I'll be glad to provide whatever else is needed. Thanks for reading.


RE: Exposure time and settings questions for newb - theskyhound - 2019-11-17

Hi John,

Thanks for the info. Its really helpful. The one thing additional that would help is the target object. Knowing this will allow me to do some checking.

Also, please open your Imaging Systems, select your imaging system, click "Save" and save it to a file. Then post the file here as an attachment. I'll check it over for any obvious problems. Note that in order to attach a file to a message here you must use the Reply button rather than type into the quick reply field.

RE: Exposure time and settings questions for newb - jonkjon - 2019-11-17


I can't believe I omitted the target object. In this case it is the Crab Nebula. I just chose it at random for testing things out. I realize it's not an ideal target for my setup but I have imaged it in the past. I have also attached the imaging system file. Thanks.


RE: Exposure time and settings questions for newb - theskyhound - 2019-11-17

Hi Jon,

The Crab nebula is a good test object though because we have full emission line data for it. I'll get back to you.