QHY6 cmount lens

[gkec]

OK I'm being a bit lazy and I just want to know.  I have a QHY6 and I want to attach a lens to it for general testing rather than having to attach it to a scope.  I believe the lens attachment is cmount is that right?  Can I just get any old cmount lens and it will "just work" or are there other things I have to take into account.

As far as I can tell the answer is yes, but as always there is some uncertainty.

[JamesF]

I think the outer thread is M42, but it is possible to get M42 to C-mount converters (such as are fitted to the ASI cameras).  There are C-mount and CS-mount lenses.  They're the same thread, but they require different amounts of backfocus (17mm vs. 12mm respectively, from memory).  So a C-mount lens can fit a CS-mount camera body with the addition of a suitable 5mm spacer (at least some of the TIS cameras have these I think).  Which will fit the QHY6 probably depends on the design of the M42 to C-thread converter.  I did try one myself recently that wouldn't reach focus, but unfortunately it's a cheap Chinese model that doesn't even say whether it's a C or CS lens and I can't remember

James

[gkec]

Yes that makes sense.  OK I need to find out the backfocus I need.

ETA back focus seems to be 14.5mm according to

http://qhyccd.com/ccdbbs/index.php?topic=1314.0

However thinking about it would an M42 lens be more suitable.?

[JamesF]

I'm not sure, but I believe the standard M42 thread you tend to get on astro gear is M42x1mm whereas (D)SLR lens are M42x0.75mm so they may well not be a good fit.  Also you'd still need to get the right amount of backfocus.  Of course there's no reason an M42x1 to M42x0.75 converter shouldn't exist.  Pentax fittings are the usual suspects for M42 lenses I think.

If it would be helpful I can try a few more lenses to try to work out what does come into focus (if anything).  You may just need to wait a few days.  My QHY6 is sitting on a shelf at the moment whilst I beat my head against an Atik 16IC.  (Couldn't get my head around what was required to get my QHY6 driver to work with 2x binning with interlaced frames, so I moved on to another problem to give my brain a break

James

[gkec]

TBH I think the interlaced operation of the camera is just broken.  I am not convinced they actually understand how interlacing works.

Having said that one of the tasks on my lists is to get binning working under Linux. 

So I'll go ahead with that and let you know what I find.  

[JamesF]

Please do.

At the moment I have it working nicely producing full-frame unbinned images on Linux (and probably OSX too though I've not done a lot of testing there) by reading two frames of half-height each and then merging them into a single buffer for a full-height frame.  I'm not sure that's the right way to do it, but it does at least produce images.

When it comes to binning though I just can't work out what it's supposed to do or if it then only returns a single frame or what

James

[gkec]

That is the right way to do it.  The device reads all the odd lines and then all the even lines.  So like you say you effectively get two frames that you have to de-interlace.

With binning the even and odd lines are combined so you get a non interlaced image. However it didn't work straight away and I found the following message in syslog:

 ERROR: Failed to read image. Got: 238592, expected 238144 

where 238144 is x/bin * y/bin - magic.  x=800 y=596 bin=2 magic=256

so I added the difference on to the image size argument in call to read_exposure and it seems to work!

[JamesF]

That's an odd number to be out.  But then the "magic" bit is strange, too.

Presumably you were using 1x binning in the X direction and 2x in the Y direction?

James

[gkec]

That's an odd number to be out.  But then the "magic" bit is strange, too.

Presumably you were using 1x binning in the X direction and 2x in the Y direction?

James

No 2x2 binning, I missed out the fact that there are 2 bytes per pixel. So it should have been :

 x/bin * y/bin * bpp - magic.  x=800 y=596 bin=2 bpp=2 magic=256

Yes it is strange. I expect if the camera source were available we would be able to understand the magic numbers better.

[JamesF]

Ah, yes, of course, it's 16-bit.  I forgot that.

James

[JamesF]

I shall have to come back to this and look at my code again.  At the moment I'm trying to get an Atik 16IC to work.  After some fighting it is at least talking to me now.  Hopefully a couple more evening's work should see it mostly sorted and I can return to the QHY6.

James