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H-Alpha Modification: Full frame or APS-C? (Sony A7iii or A6400)

astrophotography dslr imaging
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#1 ant-man

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Posted 19 September 2020 - 03:14 PM

Hello!

I have a(nother) dilemma. After deciding that I will go for an H-Alpha modification (vs. Full spectrum) of my camera since I am only interested in astrophotography, I am stuck deciding whether to H-Alpha modify my Full Frame (Sony a7iii) or my APS-C (Sony a6400).

There is the benefit of "longer reach" of the APS-C, but the Full Frame has better noise control and wider field of view, and in general I get more stable subs with the Full Frame partially because of the IBIS (in body image stabilization). However, Full Frame seems more versatile for landscapes and daytime photography so perhaps just have the dedicated astro camera with the APS-C.

After getting some moderate success imaging the Andromeda Galaxy with my Full Frame, I wish to pursue more nebulae and other deep sky objects with my telephoto zoom lens (Tamron 70-180mm f2.8). Any suggestions?

Will the APS-C have enough clarity to capture the nice reds of the H-Alpha emissions? The APS-C is also cheaper so I feel less bad in having it modified. Thank you all!

 

 

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#2 awong101

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Posted 19 September 2020 - 03:18 PM

How committed are you? Because, if you know with some certainty that one camera will reward you with less noise, I'd go with that. And from your case, you said the full frame A7iii will be less noisy? I would go with that. Focal length can be substituted/compensated one way or another.

 

Note, this is coming from a newbie who suck at post processing. So if there's less noise, I would gravitate towards that route.



#3 ant-man

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Posted 19 September 2020 - 03:25 PM

That’s what I’m afraid of! I’m also just beginning, and am not sure how long this Astro part of photography I’ll be sticking with. It’s really rewarding right now because I’m starting to make good images. In other words it’s less of a commitment to mod the APS-C. The Full frame A7iii has about 1 stop of light advantage in terms of noise. As in ISO 3200 in A7iii has about same noise as ISO 1600 in the A6400. 
 

Would that be enough of a difference to go with one over the other? Hmmm. 



#4 awong101

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Posted 19 September 2020 - 03:49 PM

Will the APS-C have enough clarity to capture the nice reds of the H-Alpha emissions? The APS-C is also cheaper so I feel less bad in having it modified. Thank you all!

 

Another nugget is, as I research my own future upgrade path, I see that most "truly" dedicated cooled camera while still being relatively affordable uses APS-C. If you go full frame now, and decide to upgrade to a dedicated cooled camera with APS-C, would you consider that as a downgrade?

 

Lastly, would this convince you? Not a great result at all, but this was shot with a WO Spacecat 51 on my DIY-HA modded Canon 60D (crop APS-C sensor)

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#5 grozmaistor

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Posted 19 September 2020 - 04:17 PM

I wouldn't mod a full frame unless I expect to obtain another FF.

Noise can be cured with more frames.



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#6 ant-man

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Posted 19 September 2020 - 05:00 PM

Ok... I think I'm set. Thanks for all your inputs. I have looked around and found some images from a Crop sensor, and yes, I think the number of subs and integration time will solve much of the noise problem. Just need good polar alignment, and perhaps manually dither my star adventurer mount! 



#7 mmalik

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Posted 19 September 2020 - 05:50 PM

Go for full-frame; choices are many (a7III, a7S, A7C). With new S and C out, others should be coming down in price, used or new. Skip crop; move forward since times are exciting. Regards

 

 

Note: Cooling is always an option which makes noise a non-issue


Edited by mmalik, 19 September 2020 - 05:51 PM.


#8 Kevin_A

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Posted 19 September 2020 - 06:17 PM

My choice would be APS-C as you will always have more scope choices if you decide on another scope in the future with no worries about if the scope image circle is big enough to cover a fullframe sensor. I usually end up cropping my fullframe images anyways and do like the apparent reach of the APS-C on smaller targets.


Edited by Kevin_A, 19 September 2020 - 06:19 PM.


#9 ant-man

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Posted 19 September 2020 - 10:23 PM

Another consideration is the filter options. It seems that for the APS-C all the clip on options is reduced to STC’s astromultispectra and the duo-narrowband. 
 

the Full frame a7 has besides those, the Astronomik filters and perhaps others as well. But overall I’ve seen great pics from the a6x00 series from Sony (APS-C). I only have the Star Adventurer too, so I’m not sure it’s possible to get over 1 minutes subs consistently without guiding. But I have a fast zoom lens (f2.8 constant). 


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#10 awong101

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Posted 20 September 2020 - 12:07 AM

Another consideration is the filter options. It seems that for the APS-C all the clip on options is reduced to STC’s astromultispectra and the duo-narrowband. 
 

the Full frame a7 has besides those, the Astronomik filters and perhaps others as well. But overall I’ve seen great pics from the a6x00 series from Sony (APS-C). I only have the Star Adventurer too, so I’m not sure it’s possible to get over 1 minutes subs consistently without guiding. But I have a fast zoom lens (f2.8 constant). 

Clip on filter isn't the best form factor. I personally find them to be annoying to use, sometimes you need to pry on them to get them to fit securely.

 

I am on Star Adventurer too, 1 minutes sub would be no problem. And if your gear isn't too heavy and your balance is good, I'd say 4minutes unguided would be the limit. (I've done 4 minutes on a horribly balanced session)



#11 DJL

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Posted 20 September 2020 - 10:31 AM

There's no easy answer - I have been going back and forwards on APS-C vs FF in Canon world, but in terms of a purchase rather than modding a camera I already own.

 

Considerations for modding the APS-C - more magnification; APS-C more easily fits into the image circle of the telescope or lens; not doing anything to your expensive FF camera that may affect daytime use.

 

Considerations for modding FF - you are using all the light that the optics can provide, as long as you verify that the image circle is not smaller than the FF sensor. For example William Optics claim that all their telescopes and field flatteners provide an FF sized image circle. Celestron SCTs also produce FF image circle but a field reducer will reduce the size of the image ciircle to APS-C and cause vignetting on FF.

 

My current thoughts are it would be disappointing to get a telescope and have less magnification than I am used to with my APS-C DSLR, so I'm heading towards APS-C. Astrobackyard.com did a lot of amazing work with APS-C, I'd suggest you check out the site and YouTube channel.




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