Exposure Starting Point

Discussion of using SharpCap for Deep Sky Imaging
jerry1
Posts: 35
Joined: Fri Dec 22, 2023 3:23 am

Re: Exposure Starting Point

#11

Post by jerry1 »

Dave,

That’s a good idea. I know how to read the histograms, but for some reason, never considered test shots. And it might be a good way to establish a “starting point” for expected exposure times as I’ve mentioned several times. Conversely, it could teach me there is no “typical” exposure for a certain celestial target at all and that every evening’s shooting session needs to be evaluated independently. My inclination is to still believe there is some typical exposure guide I can devise, though I may learn the variance is much greater than I’d surmised. Regardless, that’s a good suggestion.

Thanks,

Jerry
jerry1
Posts: 35
Joined: Fri Dec 22, 2023 3:23 am

Re: Exposure Starting Point

#12

Post by jerry1 »

Hi Jean-Francois,

I completely agree with you regarding the relationship of light gathered and focal ratios across multiple apertures and focal lengths. I’ve been considering a RASA scope or a HyperStar for some time. I’ve tended toward the HyperStar because I can remove it to use the scope’s native focal length, plus then access one or two intermediate focal lengths depending on how many different focal reducers are available for the scope.

However, the problem I always run into has to do with the arc-size of my celestial target. For planets, it’s no big deal because there are high-quality barlows available up to 5x (think Telvue Powermates) and planets tend to be quite bright with sufficient light to exploit those barlows, at least until we get to Neptune. But my primary interest is DSO, especially nebulae and galaxies. A lot of the nebulae and most of the galaxies (except in our local group) are far away and quite small as arc-size goes. So the challenge then becomes that we receive little light from them necessitating long exposures with longer focal lengths, or short exposures from lots of light with short focal length scopes, but with tiny target magnification.

You are correct that today’s smaller pixel sensors with large pixel counts do help. I think the only true cure really is a much bigger light bucket and then we no longer have portability. I’m thinking about a C11 being the largest size that is somewhat portable.

Jean-Francois , I appreciate and agree with your post. Unfortunately, I think I’m almost as far as I can go with today’s technology and that the most cost-effective approach for me is to move to a location with a better evening climate so I can capture more photons more often. Of course, that’s not cheap either, but it is becoming more appealing as I get older.

Thanks,

Jerry
jerry1
Posts: 35
Joined: Fri Dec 22, 2023 3:23 am

Re: Exposure Starting Point

#13

Post by jerry1 »

I meant to mention that if pixels get too small, that their photon collection area is also smaller and also require better seeing to resolve detail well.
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turfpit
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Re: Exposure Starting Point

#14

Post by turfpit »

Jerry

With my refractor, I have found 60x60s to be a decent compromise for objects such as M42, M31, M51, M101, M81/M82, M27 (wide field); 60x15s to be useful for globular clusters. My C8 SCT I use for lunar/planetary.

You will soon build up some knowledge after a few trials. If you have a cooled camera then a library of darks will need to be created to reflect the exposures you commonly use.

https://astronomy.tools/calculators/field_of_view/ is a useful site for checking out the framing of objects with your equipment prior to imaging.

Then you need to sort out image processing software.

The universe does not give up its secrets easily.

Good luck.

Dave
jerry1
Posts: 35
Joined: Fri Dec 22, 2023 3:23 am

Re: Exposure Starting Point

#15

Post by jerry1 »

No it doesn't. For DSO objects, I'm currently using DSS, Siril, GraxPert, and Photoshop ( I have a lot of experience with PS, but it doesn't have many tools we need for AP as you likely know). I'm also been watching video tutorials for Astro Pixel Processor and PixInsight. APP is much more logical to my mind, but PI has many, many tools, though every forum on which this is discussed mention that PI's learning curve is initially steep and frustrating. I presume that has more to do with how an individual thinks and with which paradigms they have experience with other apps. Regardless, PI seems weird to me in many ways, especially with their incessant drag-n-drop to execute every function. be that as it may, I may have to bite the bullet and go through whatever I must if I should find I need some of the tools it has that no other app supports. If so, you may hear the cursing from far away.

As for object size, I agree with you on all but M27; it's arc size is not that big. I shot it with my C8 with a 2x barlow last autumn using my 585MC planetary camera and it came out ok, but not as good as I feel it should. Both my cameras have no amp glow, so I've been shooting only flats and biases, no darks. And the 2600MC Duo is cooled and I love the camera.

Thanks,

Jerry
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