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Old 20-02-2013, 09:35 PM
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LewisM
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Took the plunge into CCD...

After using a DSLR for all my astrophotography to date, and becoming more frustrated with it, I took the plunge into a CCD - bought a Starlight Xpress SXVR-M25C OSC CCD. Be here sometime next week, fingers crossed.

My scope is a Vixen FL102S refractor, reduced to f/6.3 via a Vixen AX103S reducer. I worked out an adapter solution today so that the 2" CCD nosepiece will fit the system and be at the correct distance reducer to CCD focal plane (63.5mm).

Some general questions, being a total CCD noob:

a. would imaging GX be better done at native f/9 or reduced f/6.3 in this system? I know it is small aperture, but have to make the best I can! I typically do minimum 5 minute subs, usually 10 minute subs in good seeing.

b. SX claim this camera is ideally suited to f/5 refractor systems. What negative effects will be apparent at either f/6.3 or f/9?

c. SX also state the well-depth of the chip is very well regulated and does not bloat stars. Is this the case in practice? Will using a system outside the optimal f/5 have any effect on bloat?

Appreciate the help in this regard.
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Old 20-02-2013, 10:10 PM
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Shiraz (Ray)
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good choice.

You could happily use it at either focal length, depending on the field of view you want and the seeing. It will take about half the time to get an image at f6.3, but finest details may not be quite as well resolved in exceptional seeing. I use my QHY8 (same CCD) with an 800mm fl scope and it works fine under typical seeing at my sea level location.

The chip has pretty deep wells and an excellent anti-blooming mechanism - stars will not bloat. These CCDs are quite sensitive and produce nice clean images - you should really enjoy using it.

Last edited by Shiraz; 21-02-2013 at 05:26 PM.
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Old 22-02-2013, 08:03 AM
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rmuhlack (Richard)
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is that Brett's unit you've picked up?

according to CCD calculator (a super handy little program), the M25C will give you an image scale of 1.75 arcsecs per pixel at f9, and 2.5 arcsecs per pixel at f6.3.

You'll likely be seeing limited with both setups, while as Shiraz mentioned when the seeing is better than 2.5 arcsecs per pixel you might not get the same detail at f6.3 as you would at f9. In any case, should be a good combo i think, although be prepared that the fov will be smaller than what you currently enjoy with your full frame DSLR.
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Old 22-02-2013, 08:50 AM
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Yes, I bought Brett's. Seems I end up with a lot of Brett's gear

FOV issue not an issue to me really - the 5dMkII with FR needed such a harsh crop, the end result may well have been taken on an APS-C format camera. Less artistic licence for framing, but there are waysto compensate

I am thinking about going back to f/9 more often - especially for GX work which is my primary interest (seeing I suck at it so badly!), and back to PN imaging, when the GOOD targets pop up mid-winter again. Diffuse neb are nice and fun, but it's the PN's that fascinate me, considering the science behind them.
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Old 22-02-2013, 09:19 AM
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Quote:
Originally Posted by LewisM View Post
FOV issue not an issue to me really - the 5dMkII with FR needed such a harsh crop, the end result may well have been taken on an APS-C format camera. Less artistic licence for framing, but there are waysto compensate
Interesting. Hopefully that means that my 400D on the VC200L with a focal reducer will be a perfect fit

btw, have you experimented at all with PEC ? Using the PECPrep software that ships free with EQMOD together with a small worm backlash adjustment i have reduced my PE from ~35" peak-to-peak to about 5-6". Provided I park the scope at the end of my session i have found I can reuse the PEC training when I next take the scope out (i dont have a permanent setup in the backyard).

Now the interesting bit..... 35" of PE will be equivalent to 39 pixels with my 400D with its 5.7micron pixels on the VC200L at f6.3, while with PEC enabled that will be reduced to 6.5 pixels

On your scope, without PEC you'd be looking at a periodic error of 14.4 pixels at f6.4 and 20.5 pixels at f9 with your new CCD. *with PEC* that is reduced to 2.4 pixels and 3.4 pixels respectively.

Something to think about...
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Old 22-02-2013, 11:42 AM
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Richard, I haven't had the opportunity to use my rig for well over a month now. QLD - crappy weather one day,worse the next.

I only recently got the shoestring adapter for the mount, and was GOING to try interfacing with EQMod the other day, but never got around to it. I will be trying EVERY trick in the book as soon as I get it all going.

Shipped your robofocuser adapter today - didn't get around to it the other day.
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Old 22-02-2013, 11:45 AM
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Originally Posted by rmuhlack View Post
Interesting. Hopefully that means that my 400D on the VC200L with a focal reducer will be a perfect fit
Without the reducer, I get MINIMAL vignette on the full frame 5DMkII sensor. With the FR, the vignette is severe - at least a quarter or so of the image underexposed. That was using an FR made for Vixen's ED series of refractors, so hopefully, the vignette will NOT be as pronounced with the correct made-for FR, and the smaller chip size

I just hope I have my maths right re focal plane to reducer distance - I'll be asking a separate question about that
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Old 22-02-2013, 08:03 PM
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bert (Brett)
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Quote:
Originally Posted by rmuhlack View Post
Interesting. Hopefully that means that my 400D on the VC200L with a focal reducer will be a perfect fit
It will vignette, I had the same setup but with a 1000d. Use a flat, same goes for Lewis. It works, I know because since I owned that scope .
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