600 lens. F 5 1/30” Orion Nebula.
Posted 13 February 2019 - 10:16 PM
Should I take more lights? If we ever get a cloudless night lol.
Posted 13 February 2019 - 10:49 PM
You may have other reasons for the 1/30 second, but I think you might be able to go 1/2 second at 600mm with minimal star trails. I doubt you will get much at all at 1/30 second. Won't hurt to try though.
Posted 13 February 2019 - 11:16 PM
The max time for 'pin-point' stars is 0.49 seconds - D5300, F/5 and 600mm. Per Android Pin Point Stars app.
What ISO will be using? Take as many Light subs as you can and stack them with DSS.
Edited by Jim Waters, 13 February 2019 - 11:18 PM.
Posted 13 February 2019 - 11:24 PM
I’m going to try .50 at iso 1600. I have tried it before and got trails. If its really clear I would like to try .30 at 800. I have a Bahintov mask.
Posted 13 February 2019 - 11:59 PM
I assume its actually 0.49 sec and not 60x0.49=29.4 sec. Shoot some test shots at different speeds.
Get back to us with the results.
Edited by Jim Waters, 14 February 2019 - 12:00 AM.
Posted 14 February 2019 - 02:17 AM
With a modern CMOS DSLR you want to use an exposure time of not longer than 100 / f.l. if you really want very little to no trailing (at all). Of course, if you view the result at some smaller scale then you can expose longer and it will depend upon where in the sky you are imaging. When imaging closer to one of the celestial poles you can expose for a longer period of time (potentially significantly longer, say 2X or more depending upon your field of view).
So, using the above "rule of 100" and with a 600mm focal length your maximum exposure comes out to 100 / 600 = 1/6s ≈ 1/4s (close enough).
However, if you are imaging near to the celestial equator (zero degrees declination) with a camera that has relatively small pixels and you can't have ANY indication of trailing then you may want to use a "rule of 50."
Here is an image of the Orion Nebula that I took seven years ago using a 300mm telephoto lens on a fixed tripod using a stack of 512 images that were each exposed for 1/3s (ISO 3200, f/5.6). I wouldn't call this "good" but you can certainly see the major features and even some of the Running Man Nebula.
In any case, be careful of the total count of pictures taken with your DSLR, the focal plane shutter has a limited life span, maybe several hundred thousand activations which can go pretty fast if you are taking thousands of images each night.
Edited by james7ca, 14 February 2019 - 03:34 AM.
Posted 14 February 2019 - 03:42 AM
Of course you'll get something. The only issue is whether you will go deep enough to satisfy yourself. I suggest the following:
Determine what is the longest exposure that gives trailing short enough to satisfy yourself, at the image presentation size you are aiming for.
Use a high ISO that still seems "reasonable", e.g. 3200 for most DSLRs
Shoot as many subs as you can squeeze into the night(s) and your sky window (before Orion slips behind trees, etc.
If you have shot many hundreds of subs you may almost be satisfied with the stacked result after processing, but unlikely. If you have shot several thousand subs you are much more likely to be satisfied. This is not a case where you give up after 60 subs... Your stacking efficiency will be very low, so you really have to make up with overkill in Integration Time. One hour IT represents 7200x0.5 sec frames but because of the low Stacking Efficiency you ought to aim for several hours IT. Have a nice playnight. Hope the shutter mechanism holds up...