# APSC vs. Full Frame for Astrofotography



## Steve Dmark2 (Nov 5, 2017)

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


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## Don Haines (Nov 5, 2017)

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!


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