EdgeHD 14 / CCD Camera for Photometry??

Jack:

Pardon my comments but here goes:

1.  Most individuals may not want to tell you what to buy. If they do and you aren't happy, they look/feel bad. If you have read the documents you mentioned, you should be able to make a good decision!

2.  You have stated many reasons for not using the scope or selecting a ccd:

         0.7x reducer not good - please cite your reference - unless you approach F/3.3 to F/2 you will not see many issues that negate their use for photometry and even they can be used with care. A simple optical system (one lens or one mirror)  may be ideal but most ccd observers do not use such a system. They use what they have or can afford. You have a fine scope, make it work for you. Your photometry will be fine! Lots of observers have SCTs with reducers. The SCT is a moderately priced scope and therefore, many are used for imaging and photometry.

         there are a million different considerations - not really that many - your reading must have identified several but not a million! From your reading, why don't you state what they are?  (pixel size, FOV, QE, cooling).

         to bin or not to bin - not more than 2x2 bin - where did you get your info on this question?  please cite reference?

         I suspect/hope that you have read that you want to match your systems's pixel size with your seeing.  Have you read this? Get Ron Wodaski's CCD Calculator.Select your scope (SCT F/10). Put in reducer = 0.7. Select a ccd with pixel size, array size and binning that give you an image scale (arcsecs/pixel) that is "about" 1/2 your seeing in arcsecs.  Your seeing is probably about 3 arcsec in MD? Try to get a FOV of about 30 arcmin or so!  You want the stars on your image to fill a little more than 2 pixels. You want a FOV large enough to give you a reasonable number of comps.

3.  How much do you want to spend for the camera?  This is/may be a deal breaker?

4.  The whole thing with the 14 inch is too complicated...  It is not too complicated unless you make it that way!

So I'm steeling my self to your response.         See if these comments help as opposed to just making you unhappy!

Ken (MZK)

PS: Check out a ccd with a 6303 chip.

Jack,

Regarding Ken's comments:  Was it the Yogi who said, "I agree 100% with 95% of what he said"?  (I'm just going to quibble a little around the edges.)  Before I do that I'd like to venture the opinion that if you made a survey of all the CCD observers who submit their data to the AAVSO asking what telescope they use for photometry I'd expect the single most common answer would be the C14. 

I've used my C14 for photometry with a focal reducer (F 7.4) and an ST-9e and ST-9xe unbinned.  I've also used an ST-8xe and ST-8xme with the reducer and 2 X 2 binning.  All of these combination give excellent sampling of my local seeing.  The reducer causes more vignetting, but it also give a wider FOV.  Flat fielding, when properly done, seems to correct out the vignetting very nicely.

My only minor quibble with Ken's comments is his recommendation of shooting for a 30 arcmin FOV.

My FOV with the ST-9 was ~15 X 15 arcmin.  With the ST-8 it's ~12 X 18 arcmin.  I've never felt constrained with these FOV's, and I've always seemed to find enough comp stars.  The 6303 is a fine choice, but I wouldn't exactly call it "affordable", at least not yet.  Maybe in a few years cameras using 6303's will sell for prices now commanded by camera's with KAF 1603 chips.  

... and it's not just the camera expense.  The 1603 cameras usually use 1 1/4 inch filters.  The 6303 cameras usually use 2 inch filters- much more expensive.

If cost is not a serious constraint, by all means get a 6303 camera.  If you you have a smaller budget, I'd suggest a used camera with a 1603 chip, at least for starters.  With a C14 and the right techniques you can do very good photometry with either.

Phil

Thank you both for the thoughtful and informative comments...you've definitely given me some things to consider. That FOV software is pretty cool...using it if I get the 1603 I'd have a FOV of 11.7' by 17.6'.  I assume i'd be binning the 9u pixels 2x2 yielding 1.38"/pixel?  If I did 1x1 at 0.69"/pix that would be oversampling?? Is that FOV reasonable?

The additional costs of the 6303E are substantial but a FOV of 23.5' X 35.2' strikes me as a nice option to have.  I want to buy a CCD for photometry once....and be happy for a long time.  I have some equipment I could have a yard sale with to fund the expensive road so that's one option.

How significant is binning in this whole process?  I have a QSI 660 that for all intents and purposes has the same FOV as the 1603.  It's also ABG so I could do that linearity thing in the manual. If it was binned 4X4 I'd end up with 1.48"/pixel.  I'm sure this is a dumb question but what happens to a pixels full well when their binned?  Does the super pixel have the same value or is some approximation of the sum of the pixels?

For photmetric purposes does the NABG architecture of these chips outweigh an ABG chip to the point of avoiding an ABG chip at all costs?  I just saw that SBIG is releasing a new STXL-16200.  It has a comparable FOV with the 6303E but is ABG.  I'm intrigued with the 6u pixels...but I guess the 6303E is the place to go for photometry if I can afford it.

The last thing I'm curious about at the moment is the QE.  The 1603 max is 80% while the 6303E is 68%.  Is this a big deal?

I'm thinking that maybe it would be a very good thing for me to have a mentor sometime in the future.  I plan on taking the Photometry classes offered in CHOICE starting in April also.

Regards,

Jack

PS...Ken...I have to look through my notes to see where my questionable notions came from...thanks for setting me straight!

I have just installed a SBIG STXL-6303E [3Kx2K + SBIG filter wheel + internal guider in front of the filters] on a C14 Edge. The main constraint was Edge's short and very low-tolerance backfocus, which ruled out barrel-type focusers, so I paid up for an Atlas which I've come to love. And happily the Atlas' short travel (0.35 inches) has not been a problem--I can FocusMax at ambient temps from 33C to -15C without ever touching the mirror lock.

So this optical train is:

Edge C14 -> Celestron Edge focal reducer -> custom adapter for exact backfocus -> Atlas focuser -> [guider->filterwheel->6303E].

On very first light star shape was quite good across the image and still is. Corner vignetting is about 0.3 mag, but very parabolic so easy to calibrate away. The internal guide chip in front of the filters works very well so long as all filters are nearly parfocal. The Celeston focal reducer is specific to the Edge C14, and it's heavy, but it goes right onto the C14 so the focuser doesn't have to lift it. Pixel scale is 0.68 arcsec/pixel.

The Edge is unforgiving of backfocus, so the custom adapter and its length are crucial. I calculated the exact adapter length and used the PreciseParts website to design mine; got it right the first time which was a relief. Any system torsion must at least be reproducible, as I get TPoint models to 12-15 arcseconds all-sky.

Thought this might fill in some gaps. Cheers.
[this is my first AAVSO forum post--thanks Sara!]