Full frame or crop for astro Canon

[Craig123]

Hi all

I was thinking of trying some imaging with my SW Ed 80 pro with a 0.85 reducer and Heq5 pro.I have been using guiding with qhy5 ii and wondered which DSLR (hopefully modded) would work well with this set up...full frame or crop sensor.I remember someone explaining crop would be best but can't remember why now! Any advice much appreciated.

[Davey-T]

Crop sensor pixels generally give a better arc sec's / pixel ratio.

You can use the FLO calculator to put in various combo's

Dave

[vlaiv]

I would base sensor size on couple of parameters:

1. Budget - I would go for the biggest that fits other criteria, that I can afford

2. Corrected field of telescope system (meaning both telescope and appropriate reducer / corrector / flattener if needed).

No point in going full frame if I end up cropping final image because stars in the corners are distorted.

All of this applies if other things are equal (like pixel size, quantum efficiency and anything else I deem important in a given setup).

According to this thread:

it looks like 0.85 focal reducer will not handle full frame sensor (aps-c might even be pushing it).

[ollypenrice]

'Crop sensor' is a meaningless expression and should beat a direct path to the dustbin.  There is a relationship in daytime photography between certain ratios of lens focal length to sensor size which replicate perspective as seen by the eye. The idea is to maintain the same relative sizes of foreground to background objects as seen naked eye. In astrophotography we are working at infinity so there is no need to worry about this. Astronomical cameras come with a vast range of chip sizes and, on the face of it, bigger is better since it opens up the larger targets without the need to mosaic. But, of course, there's a 'but.' Only a minority of telescopes, most of them expensive, will cover a large sensor. Stars are very exacting targets for lenses and will show distortion at the edges long before any distortion would be apparent in a terrestrial image. So large chips are great - if you can cover them!

The issue of pixel size is best discussed separately. It defines your pixel scale and so the theoretical resolution at which you can image.

I think it is far more logical to discuss pixel scale and sensor size separately because, in principle, they are not connected. I very much doubt that the ED80 with flattener will cover full frame but do check. The corrected circle of the scope in mm needs to equal or exceed the chip diagonal in mm. Some scope manufacturers, including Takahashi, are rather optimistic on corrected circle sizes.

Olly

[Craig123]

30 minutes ago, vlaiv said:

I would base sensor size on couple of parameters:

1. Budget - I would go for the biggest that fits other criteria, that I can afford

2. Corrected field of telescope system (meaning both telescope and appropriate reducer / corrector / flattener if needed).

No point in going full frame if I end up cropping final image because stars in the corners are distorted.

All of this applies if other things are equal (like pixel size, quantum efficiency and anything else I deem important in a given setup).

According to this thread:

it looks like 0.85 focal reducer will not handle full frame sensor (aps-c might even be pushing it).

Yes..thanks vlaiv. That all makes sense and hopefully would save some cash with the cost of a smaller sensor.I will have to have a look around and see which APS C Canon would be best suited for this for low noise  

[Craig123]

3 hours ago, ollypenrice said:

'Crop sensor' is a meaningless expression and should beat a direct path to the dustbin.  There is a relationship in daytime photography between certain ratios of lens focal length to sensor size which replicate perspective as seen by the eye. The idea is to maintain the same relative sizes of foreground to background objects as seen naked eye. In astrophotography we are working at infinity so there is no need to worry about this. Astronomical cameras come with a vast range of chip sizes and, on the face of it, bigger is better since it opens up the larger targets without the need to mosaic. But, of course, there's a 'but.' Only a minority of telescopes, most of them expensive, will cover a large sensor. Stars are very exacting targets for lenses and will show distortion at the edges long before any distortion would be apparent in a terrestrial image. So large chips are great - if you can cover them!

The issue of pixel size is best discussed separately. It defines your pixel scale and so the theoretical resolution at which you can image.

I think it is far more logical to discuss pixel scale and sensor size separately because, in principle, they are not connected. I very much doubt that the ED80 with flattener will cover full frame but do check. The corrected circle of the scope in mm needs to equal or exceed the chip diagonal in mm. Some scope manufacturers, including Takahashi, are rather optimistic on corrected circle sizes.

Olly

Thanks Olly.I will look in to it.II started using an Atik 314 mono with this set up earlier in the year and intend to resume with it when it's darker but would also like to take a simpler set up to darker skies  and do a few sessions without filters and having to factor in  doing mosiacs etc..i will have to build up to that with the Atik as it sounds abit  daunting at this stage.Need to check what will fit in FOV with various DSLR  and read up some more.

Craig

[ollypenrice]

10 hours ago, Craig123 said:

Thanks Olly.I will look in to it.II started using an Atik 314 mono with this set up earlier in the year and intend to resume with it when it's darker but would also like to take a simpler set up to darker skies  and do a few sessions without filters and having to factor in  doing mosiacs etc..i will have to build up to that with the Atik as it sounds abit  daunting at this stage.Need to check what will fit in FOV with various DSLR  and read up some more.

Craig

There are really good OSC CMOS cameras now available for astronomy. ASI, Atik and QHY make them.

[Craig123]

14 hours ago, ollypenrice said:

There are really good OSC CMOS cameras now available for astronomy. ASI, Atik and QHY make them.

Thanks Olly...i had a look at a few online tonight.Do you think there will be  much difference between OSC CMOS like qhy 168c and a cooled  modded  canon from centralDS such as Canon 80d.I will try and compare as best I can with limited knowledge, I do like the idea of not having a laptop involved sometimes but it's not a major factor.Just want to avoid any more  cameras that  dont quite fit with the gear I already have like my Sony A7s.

Thanks

Craig