[Aavso-photometry] In defense of the ST-9 & CCD choiceConsiderations

[Wolfgang Renz]

Hi Michael, Hi Arne

Then please enlight us and let us take part in your experiences.

BTW:
The mentioned Apogee page says
    "A good rule of thumb to avoid undersampling is to divide your
     seeing in half and choose a pixel size that provides that amount
     of sky coverage. For example, if your seeing conditions are
     generally 4 arcseconds, you should achieve a sky coverage of
     2 arcseconds per pixel. If your seeing conditions are often 1
     arcsecond, you'll want a pixel size that yields 0.5 arcseconds
     per pixel."

So they actually don't recommen a fixed 2"/pixel, but spreading the
light (FWHM?) over (at least) 2 pixel (in diameter) to avoide under-
sampling.

Clear skies
 Wolfgang

-- 
Wolfgang Renz, Karlsruhe, Germany
Rz.BAV = WRe.vsnet = RWG.AAVSO



----- Original Message ----- 
From: "Michael Newberry" <mnewberry at mirametrics.com>
To: <mlfleenor at charter.net>; <aavso-photometry at aavso.org>
Sent: Tuesday, June 12, 2007 6:03 PM
Subject: Re: [Aavso-photometry] In defense of the ST-9 & CCD choiceConsiderations


> If CCDU makes such statements, then I would kindly suggest that Apogee's 
> website is not giving the best advice. To my knowledge, no one at Apogee is 
> an astronomer. Arne and I (and others) have "been there and done that" for a 
> lot of years. Take Arne's advice!
> 
> Michael Newberry



----- Original Message ----- 
From: "arne" <arne at aavso.org>
To: "AAVSO photometry" <aavso-photometry at aavso.org>
Sent: Tuesday, June 12, 2007 3:54 PM
Subject: Re: [Aavso-photometry] In defense of the ST-9 & CCD choiceConsiderations


> Mike, have you seriously found a recent posting or reference that
> gives a guideline of 2arcsec/pix?
> Arne

> ----- Original Message ----- 
> From: <mlfleenor at charter.net>
> To: "AAVSO photometry" <aavso-photometry at aavso.org>; "arne" <arne at aavso.org>
> Sent: Tuesday, June 12, 2007 8:45 AM
> Subject: Re: [Aavso-photometry] In defense of the ST-9 & CCD choice 
> Considerations
> 
>> > Mike, have you seriously found a recent posting or reference that
>> > gives a guideline of 2arcsec/pix?
>> > Arne
>>
>> Re: 2 arc-second/pix sky coverage  check out CCD Univeristy @ apogee's 
>> website.
>> http://www.ccd.com/ccd113.html
>>
>> In re-reading Tim’s post I see that he said 2-3  pixel sky coverage not 
>> 2. I was wanting to illustrate that as long as you are not running 
>> under-sampled that this criterion was not something that has to be 
>> explicitly followed.
>>
>> I use my SCT with a compressor and often run binned 2x2 yielding 1.24 
>> arc-sec/pix resolution or ~ 2.4 pixel sky coverage- however many times I 
>> am running 1x1 @ 0.62 arc-sec/pix  resulting in 5-6 pixel sky coverage 
>> with my typical seeing. Clearly outside of the 2-3 pixel criterion yet my 
>> results are excellent. ( I often achieve 1mmag precision with R-band 5 
>> minute averages with extra-solar planet candidates during out of transit 
>> baselines. )
>>
>> My frustration with the ST-9 was due in part to some of the images having 
>> blocky stars- I was under-sampling! I also was running @ 2260mm focal 
>> length. I could’ve run the SCT @ f/10 but here again the fov would be much 
>> too small for me.
>>
>> I do take a slight sensitivity hit but also need the resolution to resolve 
>> close stars.
>> While the ST-9 may better meet the  magic sampling requirement there are 
>> other considerations.
>>
>> I bet there are a lot more folks doing photometry with SCT’s using ST8’s 
>> instead of ST-9’s .
>>
>> Mike