APSC vs. Full Frame for Astrofotography

Steve Dmark2

EOS T7i
Mar 30, 2016
74
0
31
Germany
Hello Everyone,

I'd like to join the group of astrofotographers.
However because I'm still a birder and I absolutely love me 7D mark2 I stand before this decision.

[list type=decimal]
[*]Stay APSC and buy a wider lens
[*]Invest in a used 6D and full frame glass.
[/list]
(This is what I would have so far for Astrofotography: 7Dmark2 + Sigma 17-50 2.8 EX; 17mm x 1.6 =27mm)

to 1:
Im leaning to this lens Samyang 10mm 1:2,8 ED AS NCS CS which is ~400-450€.
This is by far the cheaper deal, because 6D plus full frame glass puts me well above 1000€.

to 2:
Full frame is already wider and has ~1.3 stops ISO advantage.

So I put up a short calculation, and I just want to show it to you.
Reason 1: Make sure I calculate correct ;)
Reason 2: If it is correct, to maybe help you with your decision.
__________

How long can I expose without getting start trails? In other words: which setting from above gives me better RAW-Data to work with.

Rule of 500:
Full Frame 6D: 500/24mm=21sec exposure.
(24mm is a middle wide full frame lens with a lot of different lenses to choose from.)

Full Frame 6D with ISO advantage: 32 sec. exposure.
APSC 7Dmkii with sigma lens: 500/1,6/17mm=18,4 sec
APSC 7Dmkii with samyang lens: 500/1,6/10mm=31,3sec

Conclusion: With both setting reacing a similar improvment, buying a wider lens for APS-C is the cheaper variant. If you guys agree with this, Im going this way.

Cheers,

Stefan
 

Don Haines

Beware of cats with laser eyes!
Jun 4, 2012
8,153
1,687
Canada
Have you considered a two step approach? Get a wide and fast FF lens ( like the Sigma F1.4 ones), use it on your 7D2, and eventually getting a FF body!