Questions about focal length, total exposure, DSLR imaging - Forums

Topic starter

Jul 17, 2020 · Edited: Jul 17, 2020

Hey! I've been wondering if it is possible to take a nice picture of the Eagle Nebula + Omega in the same field at the focal length 300mm and getting the most detail out of the pillars of creation. I know it sounds asking too much, but here's the thing: if I take shorter, but way more exposures and stack them, can I possibly smooth out the noise, will it be a way to reveal smaller details? I can't remember correctly where I did saw about the fact that more exposures tend to not only smooth noise but also reveal inner structures. Does it make any sense?
Also, about unmodified DSLR imaging: I really love the fact that when I process my Ha nebulae, I always get a blue/pink aspect; for example, carina, the lagoon, running chicken, and rosette. It's the way I edit. But I'm worried if when I modify my camera, I'll not be able to get the blue anymore since the Ha band will be dominant. Any ideas?

Engaging

dkamen

Jul 17, 2020

Hi Olga,

You can check here:

https://astronomy.tools/calculators/field_of_view/?fov[]=356||310||1|1|0&messier=16

I have put 234mm because it needs a telescope from the list to be able to share the list, so I think at 300 it would be marginal. You can probably fit them both but they would be at the edges where there is distortion and less light collection.

Best to do a mosaic.

Ha colour is not dominant with a modded DSLR, but it is more intense. Basically you have a stronger R channel, G and B are not affected. So you do not lose everything but it will be more difficult getting the colour balance right. Blue will be blue, green will be green but pink, orange and purple will shift to red.

If you like your unmodded DSLR then it's not worth it, after all not everything is Ha.

Cheers,

Dimitris

Helpful

dkamen

Jul 17, 2020

Oh and the bit about multiple exposures revealing detail is right but there are diminishing returns: From 10 exposures to 100 you get an improvement. To get the same improvement from 100, you need to go at 1000 which can be very tricky to process with DSLR sized images. And you should always select the good ones because a bad exposure will remove detail. Also the exposures should be long enough and with high enough ISO to record significant signal, higher than your sensor's read and thermal noise.

IMO best approach for hundreds of thousanfs of subs is to integrate and remove light pollution from each night separately (making sure you have about the same total time per night), or in groups of say 50-100 and then integrate the integrations. 5x(100) is much easier than 500.

Helpful Insightful

Related discussions

Dark, Flat and Bias Frames on Sigma 100-400 DG DN OS for DSO

Hello People, I know this have been asked before here and is widely talked about over the web however I am little confused with the information I have come across so posting it here for more clarity. I have a Sony A7III w/ Sigma 100-400 DG DN OS lens...

Calibration frames improve stacking quality and reduce noise in deep-sky astrophotography.

Jun 7, 2022