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NAN: CCD + Pentax 6x7 (new project)

Dangerous-Dave

By Dangerous-Dave
in Imaging - Deep Sky

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Dangerous-Dave

Dangerous-Dave

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Hi folks, here's a shot from my new widefield CCD "project",

ngc7000ha28x600s1.jpg

Starlight Xpress SXV-H9 CCD, Astronomik 12nm Ha filter, Pentax 6x7 200mm/f4 lens at f4, 28x600s.

OIII and SII to follow.

Here's the rig for those interested. The silver rings are the Teleskop Service Telefokus105mm micro-focuser/lock for tele-lenses, an excellent piece of kit I would thoroughly recommend.

200mm/f4 lens:

4849342059_c51b7623de_b.jpg

300mm/f4 lens:

4818022214_0ea2b1eec1_z.jpg

T2:6x7 adaptor (custom made from a 6x7 extension tube by SRB Griturn):

4850206076_964cb9fe9c_z.jpg

The whole rig, including mount, can't have cost much more than a couple of grand.

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Psychobilly

Psychobilly

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I think medium format lenses are the way to go for ultra-wide CCD shots.

Indeed - How flat was the field - i would expect it to be very good ...

Already started machining - making a set of Scope ring at the same time... picked up a 100mm offcut of nice thick walled ally tube up from the metal stockholder on the way home for £5 and got the nylon thumbscrew on the way as well :)

Peter..

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Dangerous-Dave

Dangerous-Dave

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Indeed - How flat was the field - i would expect it to be very good ...

Already started machining - making a set of Scope ring at the same time... picked up a 100mm offcut of nice thick walled ally tube up from the metal stockholder on the way home for £5 and got the nylon thumbscrew on the way as well :)

Peter..

The 300 is great Peter, the 200 not so good - evidence of mis-shaped stars on the left of frame - actually the top in this shot as I've rotated it so it's the usual "Canada-upwards" orientation. It could be the adaptor isn't perfectly straight, where the new T2 part meets the 6x7, and needs a shim.

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davew

davew

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Hi Dave,

Looking at your setup, I notice one ring holds the adaptor and one the camera. Is there a chance they are being pulled out of line ? You also have the filter wheel to add to the mix.

But hey, 600s at f4. Brilliant. Love it.

Dave.

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Dangerous-Dave

Dangerous-Dave

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Hi Dave,

Looking at your setup, I notice one ring holds the adaptor and one the camera. Is there a chance they are being pulled out of line ? You also have the filter wheel to add to the mix.

But hey, 600s at f4. Brilliant. Love it.

Dave.

Good thinking Dave. :D The rings use a single bolt each so may well not be parallel, and any discrepancy on the adjusting bolts could be flexing the system. Now how the heck do I rectify that...:)

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davew

davew

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Hi Dave,

What I've seen done in a few photos is.... 2 rings holding the scope, then a further ring holding the camera. This would be possitioned after a few test runs to get the thing straight.

However, you don't have a long scope.

One idea that springs to mind is slightly extending the mounting plate and fitting the two rings to the camera. This hopefully sorts the camera and filter out. Then a further ring to hold the lens / adaptor. Then test and test again.

I realise this would be a faff and costs but from what I see you've already done I don't think it would put you off.

It's an idea anyway. Some one may have a better fix.

On the other hand it could be a squint adaptor :)

Dave.

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Dangerous-Dave

Dangerous-Dave

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Hi Dave,

What I've seen done in a few photos is.... 2 rings holding the scope, then a further ring holding the camera. This would be possitioned after a few test runs to get the thing straight.

However, you don't have a long scope.

One idea that springs to mind is slightly extending the mounting plate and fitting the two rings to the camera. This hopefully sorts the camera and filter out. Then a further ring to hold the lens / adaptor. Then test and test again.

I realise this would be a faff and costs but from what I see you've already done I don't think it would put you off.

It's an idea anyway. Some one may have a better fix.

On the other hand it could be a squint adaptor :)

Dave.

You're right, I've not really got anywhere to put a third ring! :) Also, if the flex is between the filter wheel and lens adaptor (or filter wheel and CCD) as I suspect, then would adding another ring to one side actually resolve that?

I was thinking about pointing the CCD at a large open cluster, setting it on a loop, and tinkering with the lens end ring to see if/how it affects the star shapes. That ring grips the adaptor rather than the lens so it shouldn't stop me changing lenses.

The mis-shapes all appear to be in one direction which suggests misalignment rather than coma. Is there anyone with CCD inspector who could kindly run my shot through that? :D

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davew

davew

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If it could be made to fit (?) then 1 ring on the camera right next to the wheel and 1 ring right at the other end of the camera. Make them a solid fix. Then 1 ring on the adaptor or lens and manoeuvre up/down/left/right until set.

Also what I'm thinking is that your lens is very heavy. If you image say lowish in the east, the joints may open. Go straight up and they all close in a straight line.

Am I being a bit retentive here ? Don't answer that.

Dave.

The reason I'm trying to nail this with you is that the Ha shot is one of the best of it's type I've seen.

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barkis

barkis

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"I see you caught a pic of your obsy outside in that 1st equipment pic "

Hahaha! @ obsy - sorry - had to laugh at that comment. But lovin the rig and the pic :p

Yes, I spluttered a few Corn Flakes out when I read that comment.

Very Amusing.

Looks like a wnning combination you've put together Dave.

All those large Nebs. have nowhere to hide now.

Ron.

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