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First light QHY8 - M42

MartinB

By MartinB
in Imaging - Deep Sky

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MartinB

MartinB

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Finally more or less sorted with the QHY8 although still on the learning curve. Surprised to find it clear at about 9.o'clock last night set up and went for a bright blousy DSO to start off with. All a bit of a rush before it disappeared behind the house but got 10 x 3 mins 10x2mins and 12 x 1 min (was experimenting!). Lumped them all together in maxim. Taken with a William Optics FLT 110 apo with a TMB designed triplet lens on loan from Steve at FLO Also using the TMB field flattener.

1st impressions of QHY8 - a tad less sensitive than SXV H9 but no surprise there. The field wasn't flat, anything but, which surprised me, perhaps I'm doing something wrong with the flattener, plus significant vignetting.

I'm very pleasantly surprised by how much has been pulled out with about an hours worth of a hotch potch of subs. The camera seems pretty light on blue - scaled up 40% during debayering. No LP filter.

Processing very slow with the big files and my old computer.

4077_normal.jpeg

(click to enlarge)

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barkis

barkis

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Yes it's nice to see you are up and running again Martin. Your processing is great when the image is produced with everything of interest encompassed in it. This is the magical part as far as I am concerned. A one shot LX exposure to acquire an image like that, would have scorched the central part of this subject. It is wonderful creation to me, but you are seeing the image through more experienced eyes.

You and the camera will make a great team, as it is with SteveL and his.

Also, I think Steve Flo. is going to have a job wresting that Triplet away from you. :D

Ron. :lol:

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steppenwolf

steppenwolf

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This is very nice, Martin and I am pleased to see that you are finally up and running with the camera. Vignetting is something not to be taken lightly and it is going to be a serious consideration in my next purchase (which will be a larger format sensor). Although flat frames will disguise the problem, the lack of photons is still there (or not there if you see what I mean!) - I guess this is why we are now seeing 4" focus tubes!.

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MartinB

MartinB

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Thanks guys. A lot of the dim detail doesn't show up on my cruddy work monitor so I might give it a bit of a power boost.

Huraah! Nice to see you up and running again :D What was the issue with the camera first time round? (and yes, its not so sensitive in blue)

I couldn't get it to produce an image Steve. It would with the focusing software provided but not in Maxim, just a bright line down 1 border. Not heard of anyone else having similar trouble. I've installed Tom's drivers and everything seems fine now. I'll be PMing you some time for more technical advice!

Vignetting is something not to be taken lightly and it is going to be a serious consideration in my next purchase (which will be a larger format sensor). Although flat frames will disguise the problem, the lack of photons is still there (or not there if you see what I mean!) - I guess this is why we are now seeing 4" focus tubes!.

The FLT110 has a 4" draw tube. It makes for a very stiff set up which is handy if you have heavy imaging kit but not sure whether it helps reduce vignetting or not. I think I probably had the TMB flattener set up incorrectly. I didn't pay any attention to spacing (which is apparently optimized for DSLRs) so would need some attention if I were keeping this scope, which I can't sadly - it's returning to it's rightful owner this week :sad11:

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SteveP

SteveP

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Martin

What a great shot of M42!

As a newbie to this hobby and keen to understand more, can you explain what you mean by

'The field wasn't flat, anything but, which surprised me, perhaps I'm doing something wrong with the flattener'

I'm not sure I can see anything which suggests it isn't flat! Please enlighten

Steve

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MartinB

MartinB

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As a newbie to this hobby and keen to understand more, can you explain what you mean by

'The field wasn't flat, anything but, which surprised me, perhaps I'm doing something wrong with the flattener'

I'm not sure I can see anything which suggests it isn't flat! Please enlighten

Steve

Steve, the focal plane of light falling on the camera chip is curved which causes 2 problems. If the image is focussed on the centre, stars at the periphery will be slightly out of focus. A more noticeable problem is that the light is coming at the chip from a small angle of perpendicular which causes the stars to be mis-shaped.

the image has been greatly reduced in size for posting here. On the full size original the stars are distorted at the edge but the problem isn't obvious in the image posted here.

The way to fix this problem, with a refractor, is to place a lens quite close to the end of the imaging train. This corrects the curvature to produce a flat field. I was using a TMB flattener specially designed for the scope. I think the spacing is quite important and I obviously got this wrong.

Here is a graphic representation of the field flatness using software called CCDInspector

4093_normal.jpeg

(click to enlarge)

The problem is much less with smaller chips. Here's what I get without the field flattener but with a camera with a smaller chip - the SXV H9

4094_normal.jpeg

(click to enlarge)

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centroid

centroid

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That's a good start Martin, so welcome to the world of OSC imaging :D

It was interesting to hear that the CCD is 'light' on the blue. Is it not the same 'chip' as used in the H9C?

If so, then its not directly related to the 'chip', as I never have to adjust the colour balance on any images from the H9C.

Dave

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MartinB

MartinB

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It's the 6 megapixel Sony ICX chip Dave. Same as in the M25 as Steve says.

Dave, I think you should check out the blue sensitivity thing since my impression is that the H9c is weaker in blue. The M25 and H9c chips are from the same Sony family and my guess is that they will have very similar behaviour. Both you and Steppenwolf have produced lovely M81 images but, to my eye, have been lacking in blue. I had a good look at Steve's M81 posted JPEG (not an ideal thing to do I know) since I thought parts of it were too red. I couldn't bring out any blue at all. I would be very interested to see what you could come up with by scaling up your blue channel by 40%. Those outer lanes should have a definite blue tinge to them coming from the areas of hot new star formation.

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