This is first light tonight using an MPCC on the 12"
Newt and the QHY-8/ homemade GEM.
I now get almost full frame illumination (I think)
and it shows the extent of the typical fast Newt
coma.
The colour balance is wrong here but I did do a sky
background auto-adjust. No sharpening has been applied here,
seeing is average to bad and the gully breezes are gale force.
Excuses
I have a collimation issue too!
Edit: Question for the QHY-8 gurus:
Do you guys capture in RAW FITs with these OSCs and process
as Raws minus Raw darks etc
OR do you capture in RGB FITS and RGB Darks?
The processing regime last night took AGES to do just 35 frames.
I did this:
RAW capture ---> square debayer minus debayered darks--->stacked.
This is first light tonight using an MPCC on the 12"
Newt and the QHY-8/ homemade GEM.
I now get almost full frame illumination (I think)
and it shows the extent of the typical fast Newt
coma.
The colour balance is wrong here but I did do a sky
background auto-adjust. No sharpening has been applied here,
seeing is average to bad and the gully breezes are gale force.
Excuses
I have a collimation issue too!
Comments and suggestions welcome.
Steve
Hi Steve. there is a lot to look forward to in that combination of scope/mount/camera. I think I would put the coma issue at the top of my list of things to fix. I'm more than surprised the MPCC didn't take most of it out. So I have to ask a question about how you have attached it to the camera. Have you maintained the 55mm separation required between MPCC and CCD? That's a must.
Peter
QHY8 is a DSLR sized chip and if I recall correctly is the Sony 6.3mp chip first used in the Nikon D70.
So it is what is termed in the CCD world as large format.
This then requires coma correction from your Newt in a circle wide enough to fully illuminate your chip with a fully corrected image. This is referred to as the corrected circle or corrected field. It has a dimension like 36mm etc.
The MPCC per the Baader website will correct even 35mm film size (44 x 44mm I think it is) which is bigger than your chip of 21 x 14mm.
I looked up the MPCC specifications and as pointed out you need to have it set 55mm from the back metal flange of the MPCC
to the top plane of the chip. This is called metal back distance (the last metal edge of the corrector to the surface of the CCD chip).
All correctors/flatteners have a metal back distance. You then need to have the correct length adapter to make sure your MPCC and chip are set at that distance. If one is not available standard you'll have to get one made up. Hopefully QHY sells accessories or Baader does.
There is mention on the Baader site about a T2 system.
I looked up the MPCC specifications and as pointed out you need to have it set 55mm from the back metal flange of the MPCC
to the top plane of the chip. This is called metal back distance (the last metal edge of the corrector to the surface of the CCD chip).
All correctors/flatteners have a metal back distance. You then need to have the correct length adapter to make sure your MPCC and chip are set at that distance. If one is not available standard you'll have to get one made up. Hopefully QHY sells accessories or Baader does.
There is mention on the Baader site about a T2 system.
The unit does not operate properly at the wrong spacing.
Greg.
Thanks Peter and Greg for the advice.
Yep I had read about the 55mm distance but I just threw it straight
on to get an idea of the 'uncorrected coma'/ rough FOV of my 12".
I knew it was going to have some but I didn't quite think this much
If I am correct I need to knock up a quick spacer today on the lathe
with the spacing being 35 mm as shown below in red mm.
The QHY-8 has a CCD/film plane depth of 20mm from the face
of the 2" nosepiece.
I hope I have this right.
I have 2 options for threads....42mm male one end, 48mm female other.
OR
42mm male one end, 42mm female the other (with spacer/lock ring
removed on the MPCC)
Thanks Peter and Greg for the advice.
Yep I had read about the 55mm distance but I just threw it straight
on to get an idea of the 'uncorrected coma'/ rough FOV of my 12".
I knew it was going to have some but I didn't quite think this much
If I am correct I need to knock up a quick spacer today on the lathe
with the spacing being 35 mm as shown below in red mm.
The QHY-8 has a CCD/film plane depth of 20mm from the face
of the 2" nosepiece.
I hope I have this right.
I have 2 options for threads....42mm male one end, 48mm female other.
OR
42mm male one end, 42mm female the other (with spacer/lock ring
removed on the MPCC)
Steve
Someone in these you forums (I can't remember who I'm afraid) had a spacer made up that had a threaded male/female section in the middle, with a locking ring so that you could fine-tune the separation if you wished. Seemed like a good idea and since you're heading to the lathe anyway, this might be a good plan.
Peter
Someone in these you forums (I can't remember who I'm afraid) had a spacer made up that had a threaded male/female section in the middle, with a locking ring so that you could fine-tune the separation if you wished. Seemed like a good idea and since you're heading to the lathe anyway, this might be a good plan.
Peter
Yes thanks Peter, I was messing with alu stock just a few mins ago
thinking the same...but it has to also slide down the 2" focuser too
so low profile lock ring of some sort....or recessed grub screws.
Yes thanks Peter, I was messing with alu stock just a few mins ago
thinking the same...but it has to also slide down the 2" focuser too
so low profile lock ring of some sort....or recessed grub screws.
cheers,
Steve
Yeah. When you're cutting the femail thread, just cut it 5-10mm deeper and cut that extra off - that'll be the locking ring - making the male thread a but longer too of course. That'll keep the OD to the right size.
Peter
Steve,
your debayering seems wrong to me. With QHY8 Eta should be dominated by RED channel, not blue. Make sure you find the 'offset' information in whatever software use for debayering and set it correctly for QHY-8.
Someone in these you forums (I can't remember who I'm afraid) had a spacer made up that had a threaded male/female section in the middle, with a locking ring so that you could fine-tune the separation if you wished. Seemed like a good idea and since you're heading to the lathe anyway, this might be a good plan.
Peter
Marc Aragnou (Multiweb) posted pics of his adjustable spacer around August last year. I am sure he can send them to you if you PM him.
G'Day Steve, Just had a look at the image. A couple of things may be worth thinking about.
1. Send me a PM with your address and phone no. I will give you a call.. I think I still have a custom spacer for the MPCC and QHY8 and I will send it over to you.
2. Debayering, I'm not sure what you used for capture or deybayering your image but it does look somewhat blue. If you are using Nebulosity the debayer protocol used for the QHY8 is incorrect. You have to go to options and check the manual debayer override to set the correct sequence. The correct sequence is x = 1 , y = 1 with a pixel size of 7.8um.
3. Search these forums for custom MPCC adapter as Marc (multiweb) arranged to get a custom adapter made for the MPCC which was adjustable and from memory he was very happy with the end result and I recall him posting a drawing of the adapter which you could probably make yourself.
I always capture in undebayered Raw images in all capture programs.
Cool shot Steve. I think your MPCC spacing is incorrect and you debayered to the wrong matrix too. QHY8 is RGGB.
Calibration is before debayering. So you shoot your lights in raw FITS 16bits (approx 11MB each). You shoot your bias frames in raw fits and shoot your bias in raw fits too. You do your calibration on your lights with the bias and flats as they are. (with bayer matrix).
Then you debayer to Red, Green & Blue in separate directories. Pick the best FWHM frame in each channel and do your alignment/normalisation/date rejection per channel. WHen you have your masters R, G & B you recombine to color then save as TIFF 16bits scaled. Go to PS and season to taste.
PS: DO NOT align any light/flat or bias with the bayer matrix in. Only align debayered subs.
Last edited by multiweb; 06-02-2010 at 05:18 PM.
Reason: clarification
Thanks for the input fellas....I shoulda checked in for replies early
afternoon...cos I've just made one Marc, Doug, Pete and Trevor!
I made it adjustable so that it covers approx 52-57mm.
Locked with a recessed pair of grub screws that won't foul with
the 2" Drawtube. Thanks Dougie for the offer though mate
I will have to make a few of these separate distance spacers for any 2"
eyepieces I ever buy, not that I do much visual.
The only one I have is the GSO 32mm, might be interesting to try
the MPCC on that. I do remember my first view of Eta Car through that
when this mirror was brand new, and the coma was evident 7/8ths
out to the edge of the FOV.
Thanks Doug and Marc re the debayering....yep I just did RGB..that would
explain quite a bit
I'll sit down and read your tips guys and try and digest the method
you use. Who would have thought the OSC would be such a learning
curve when going from DSI II mono . Not that I've been very successful
with that either
Quite a lot of QHY8 +MPCC's getting around now, would you be interested in quoting a price to make your adaptor?
Mike
Make that 2:
By the way - that is a nice, polished (i.e. highly reflective) inner surface on the adapter. You migh want to think iabout cutting in a nice fine pattern of parallel ridges and follow with a coat of matt black blackboard paint or equivalent. The QHY8 has enough reflexions already!!
In all honesty, without checking, these things probably go for under
$50 posted, or I wouldn't pay any more, put it that way.
It would cost $20 bucks driving around finding suitable alum stock
to make a few and that's before I added my machining time.
If I were you I would buy one, it would be in the post 2 days later
and probably better tolerance and finish than mine
Have I talked you out of it yet
As for reflective innards, all you can see in the pics are the M42 thread
surfaces and the inner and outer inteference fit sleeve.
The bore is a vee shaped tool run on slow thread cutting down the guts
as I do all my adaptors. Flat black paint and texta to touch up.
Sweet as.
Tonight's effort,
the 55mm spacer now in use. Coma is minimal but I still have
the elongated stars I've had all along radiating in a position angle
sort of 10 o'clock. This is NOT a tracking issue. It's on a live 1 sec shot
or a 10sec shot. Maybe the CCD is slanted slightly? A tip from Theo on it
here:http://qhyccd.com/ccdbbs/index.php?P...a&topic=1885.0
That and a weird sideways blooming effect on Eta
and a few brighter stars. Debayer artifact?
Seeing was not brilliant either tonight but I think I nailed the colour
albeit a bit unsaturated and lacking blue.
The debayer was done as per Doug and Marc's suggestion 7.8u sq
pixels with a 1x1 ratio.
Edit: 2nd result: 2 iterations of the same curve applied.
