How easy would it be.......

[laser_jock99]

....to remove the IR/UV filter from one of these:

Sony A7R

I'm attracted by the idea of full frame 36MP astro imaging camera for just over £1k

The other features of interest are:

1) No anti-alias filter = sharper stars

2) No mirror = flange-to-CCD distance of only 18mm (compared to 46mm on Nikon/Canon). This would make getting your filter wheel & OAG in place a breeze.

3) Light weight, only 400g

4) Tilting Live View screen

Sony A7R spec http://www.sony.co.uk/electronics/interchangeable-lens-cameras/ilce-7r

Any thoughts?

[Scott]

sorry, I can't help with that camera but what filters would you be using for a colour camera? also, what's the software (astro) like for the sony?

I'm not trying to be clever? I honestly haven't a clue

[nmoushon]

I used a sony for a while. Just as good as my 450D but I never used any software for either, just the handheld controler. This would be a gamble as I dont think anyone has tried it before so you would be a first. At least I havent seen anyone try yet. So no guides to go off of. Its a lot more compact than regular DSLRs so I'm sure that the existing guides wouldnt be much use. Also I would think that that little hand grip might get in the way of any filter wheels though you might be able to use a spacer.

[tahoetomahawk]

I have a Sony NEX-C3 without the IR or UV filter. I got it on eBay from a shop that does the conversions.

[pete_l]

I'm attracted by the idea of full frame 36MP astro imaging camera for just over £1k

Any thoughts?

I don't think merely taking the front filter off would turn this camera into a "astro imaging camera".  Yeah, sure full-frame.

But to get the benefit of that you need a scope with a wide enough aperture at the eyeball end so that you don't get vignetting.

Plus you still only have a "room temperature" camera - with all the noise that implies for long exposure photograhy.

And really, who needs a 36 MPixel image? Even top of the range 4K monitors only have about 8 million pixels. So you'll never get to see the full image and if you start cropping it, there's no point having a full-frame.

[laser_jock99]

Just mulling over the feasibility really.....

sorry, I can't help with that camera but what filters would you be using for a colour camera? also, what's the software (astro) like for the sony?

I'm not trying to be clever? I honestly haven't a clue

Filters- hopefully won't need these as I'd be shooting OSC from a dark sky site (Bortle 6-7).

Software? I think these are design to be remotely controlled via a smartphone app. I can't find an aftermarket intervalometer yet which would be my preferred route.

I used a sony for a while. Just as good as my 450D but I never used any software for either, just the handheld controler. This would be a gamble as I dont think anyone has tried it before so you would be a first. At least I havent seen anyone try yet. So no guides to go off of. Its a lot more compact than regular DSLRs so I'm sure that the existing guides wouldnt be much use. Also I would think that that little hand grip might get in the way of any filter wheels though you might be able to use a spacer.

Good point about the hand grip- some of the 18mm back focus would be lost to that. 

I don't think merely taking the front filter off would turn this camera into a "astro imaging camera".  Yeah, sure full-frame.

But to get the benefit of that you need a scope with a wide enough aperture at the eyeball end so that you don't get vignetting.

Plus you still only have a "room temperature" camera - with all the noise that implies for long exposure photograhy.

And really, who needs a 36 MPixel image? Even top of the range 4K monitors only have about 8 million pixels. So you'll never get to see the full image and if you start cropping it, there's no point having a full-frame.

Filter removal would make it 'full spectrum' - but I'm really only interested in the near IR part (Ha)

Regarding coverage of the 'full frame' CCD only two of my scopes could do that as they have 3" focusers. Even then I would probably need to get an ASA 3" Wynne Corrector which would cost as much as the camera!!

Ambient temperature yes- but cooled OSC 35x24 cameras are considerably more ! Other 'full frame' DSLRs are way more expensive and have 46mm of unusable back focus.

The big CCD would give a wider FOV (assuming you have a fully corrected imaging circle). I take your point about the image size though- I have never posted anything greater than 1024 x 768...........

[ronin]

I have an A350 and asked Sony for the filter specification.

They could not tell me what it was and so where it actually cuts off.

The "assumption" being it is the same as the Canon IR filter however it may not be.

If Sony install a filter that cuts at 700nm not the 650 of the Canon then wou would not really need to remove it.

In effect the fiorst question is what is the filter characteristics and does it need to be removed?

[Steve Ward]

According to this the A7R  has no low pass filter ...? ... http://www.dpreview.com/reviews/sony-alpha-a7r

[laser_jock99]

I have an A350 and asked Sony for the filter specification.

They could not tell me what it was and so where it actually cuts off.

The "assumption" being it is the same as the Canon IR filter however it may not be.

If Sony install a filter that cuts at 700nm not the 650 of the Canon then wou would not really need to remove it.

In effect the fiorst question is what is the filter characteristics and does it need to be removed?

If I did acquire one (big IF at the moment) then I would test it un-modded first. No point nullifying the warranty (such as it is at Grey Import prices) for the sake of a bit of testing.

Looking at the few available web astro images then I'd say it does need modding

un-modded

[ronin]

I would suspect that the filter is very similar to the Canon, it was just a thought when I bought a T-ring for mine that whatever Sony fit may be better for pointing at the sky then what Canon fit.

If you see the Canon transmission curve then even a shift of 20nm would be very useful.

So I asked Sony UK, they didn't know and informed me they were asking Sony Japan.

Eventually I had a reply saying they could not obtain/did not know the information.

I actually think they did say they did not know.

Someone in Sony must know what the filter characteristics are.

May ask again one day, did try a few of the camera sites, think I was the only post on the Synax site that had no replies.

[laser_jock99]

I would suspect that the filter is very similar to the Canon, it was just a thought when I bought a T-ring for mine that whatever Sony fit may be better for pointing at the sky then what Canon fit.

If you see the Canon transmission curve then even a shift of 20nm would be very useful.

So I asked Sony UK, they didn't know and informed me they were asking Sony Japan.

Eventually I had a reply saying they could not obtain/did not know the information.

I actually think they did say they did not know.

Someone in Sony must know what the filter characteristics are.

May ask again one day, did try a few of the camera sites, think I was the only post on the Synax site that had no replies.

I suspect the filters are similar. The spectral response curve of the bare CCD's will differ though. I can't find any information on this CCD on the web at all.

The quick way to find out would be to buy a camera and do some 'before & after' tests probably.

The main thing stopping me doing this is that without further significant investment I can't easily fully illuminate a 35mm CCD with a corrected flat field. My Baader MPCC III coma corrector claims a flat field imaging circle of 44mm (just about a 35mm CCD diagonal) but I don't know if this would work in practice?

I could test it first using an old 35mm film camera I suppose?