14" SCT and Sony a7s - a good match?

[gorann]

I recently aquired a Meade 14" LX200R f/10 (unforked so now on an EQ8) and want to find a camera for it with a big pixel size to give me a reasonable pixel / arc second resolution, i.e. around 1 "/pixel. Except for a few mainly old CCD cameras, most available CCD and CMOS cameras have pixels between 2.4 and 5 uM, so unless I do binning I end up with image scales between 0.14 and 0.3 um/pix which is a rediqulous degree of oversampling.  It struck me that the Sony a7s that has now been around for a while, has a good reputation for low noise and high sensitivity, has biggish pixels (8.3 um on its 12 Mb full APS sensor), and is now relatively cheap (1000 GBP for a new one here in Norway). It would give me about 0.5 "/pix (0.9 "/pix with a reducer), which is reasonable. Now when I search on images taken with the Sony a7s on Astrobin I find that it is almost exclusively used on wide angle lenses (telephoto)  leading to an extreme under-sampling of 5 - 10 um/pixel or more. Very few images are from larger telescopes and unfortunately most of those are far from great but I suspect that this could be more about the skills of the photographer than the equipment.

So, am I missing something? Should not the Sony a7s with its big pixels be one of the best matches (if we talk DSLRs) that I could get for a big SCT?

[DaveS]

Unfortunately big pixels now mean big money, as in 16803 cameras, though I note Moravian still do 11000 based cameras, both having 9 uM pixels.

[thomasv]

Are you aware of the Sony "star eater" issue, search it up if you aren't. I don't know exactly how big of an issue is for long focal length. 

Also, of course you'd need to consider modding it if you want good Ha sensitivity. 

 

[gorann]

4 minutes ago, DaveS said:

Unfortunately big pixels now mean big money, as in 16803 cameras, though I note Moravian still do 11000 based cameras, both having 9 uM pixels.

Yes, I know Dave, so the Sony a7s could be a bargain, maybe.... Big pixel cameras are nothing that the mass market ask for.

[gorann]

Just now, thomasv said:

Are you aware of the Sony "star eater" issue, search it up if you aren't. I don't know exactly how big of an issue is for long focal length. 

Also, of course you'd need to consider modding it if you want good Ha sensitivity. 

 

Yes, I have heard of it (an algorithm to reduce bad pixels) but as you say it is probably less of an issue for long FL. The camera is widely used for short FL astrophotography so if it still exists it may not be a major issue.

[DaveS]

The Sony could be an option, especially S/H but as Thomas has said, be aware of the "Star Eater" problem. The only other Big Chip / Big Pixel camera that immediately comes to mind is the original Canon 5D, but that's so ong in the tooth as to be barely worth considering, even S/H. I do have one, and did my first steps into AP with it.

[gorann]

3 minutes ago, DaveS said:

The Sony could be an option, especially S/H but as Thomas has said, be aware of the "Star Eater" problem. The only other Big Chip / Big Pixel camera that immediately comes to mind is the original Canon 5D, but that's so ong in the tooth as to be barely worth considering, even S/H. I do have one, and did my first steps into AP with it.

Sorry Dave, but what is S/H? (maybe should now but it is gettinglate here)

[DaveS]

Sorry, Second Hand.

[gorann]

10 minutes ago, thomasv said:

Are you aware of the Sony "star eater" issue, search it up if you aren't. I don't know exactly how big of an issue is for long focal length. 

Also, of course you'd need to consider modding it if you want good Ha sensitivity. 

 

Regarding Ha, I am not that worried. It has a reputation of being extremely light sensitive (you can use high ISOwith little noise) so it will probably pick up enough.

[gorann]

1 minute ago, DaveS said:

Sorry, Second Hand.

Well, I just found that a major photo chain in Norway are now selling new ones (probaby the very last ones) from the first generation (Mk I) quite reasonably (1000 GBP compared to the 1700 they used to ask)

[alan potts]

I have a Brightstar Mammut with large pixels which I believe are 8.6x8.3 or similar, but it is a very small chip and more suited to being a guide camera maybe. It was bought for my 12 inch SC and never used. It would probably do a job if you could ever locate a target on the chip.

Alan

[gorann]

11 minutes ago, alan potts said:

I have a Brightstar Mammut with large pixels which I believe are 8.6x8.3 or similar, but it is a very small chip and more suited to being a guide camera maybe. It was bought for my 12 inch SC and never used. It would probably do a job if you could ever locate a target on the chip.

Alan

Yes, there are a few affordable cameras with small chips and big pixels. But as you say it would not be easy to find anything on a small chip at 3.5 m focal length, so I really need a big chip. The FOV is small enough as it is. The Sony a7s has a full sized APS chip (44 mm diagonal) so it will cover the whole image circle and there would be some vignetting and  I would probably have to crop a bit away, but that is OK.

[alan potts]

Gorann,

I have a mate that has a s/h camera business, I had masses of kit from him between 98 and 2013 when I did a great deal of MF photography as well as 35mm and digital. His name is Malcolm Collins and the business is Camtech Cameras in Cotterham near Cambridge. He has some of the keenest UK prices and is very dependable, worth dropping him line or phoning, he will send out but of course a charge, last time to me it was 20 quid for a body (camera that is).

Alan

[michael8554]

The experts will doubtless have an opinion worth listening to, but I believe your large oversampling may be less of an issue than you think. 

The inherent sensitivity of the camera will certainly help to overcome any loss due to the pixels being too small. 

Large undersampling would be more of a problem IMO. 

Michael 

[gorann]

Thanks for all the input guys! I am an optimist so I just ordered a Sony a7s with only 985 exposures (= in as new condition and still a years warranty) from Germany (ebay). I will keep SGL updated on how it performs on the big SCT.