[Aavso-photometry] binning considerations

[Wolfgang Renz]

Hi David

If you really consider serious U Band photometry a mirror-only
scope will be the best choice as any glas (if its not quarz or
fused silica will absorb 100% somewhere in the range of
300-400nm) and its coating (usually optimized for the visual
range and reflecting more than uncoated glas in the NUV
and NIR) will absorb most of the far NUV light in the U band
(e.g. Jeff Hopkins gets about twice as many photons in the U
band with his good old orange C8 than with his new M8 with
UHTC).
But some "advanced" (for the visual range) mirror coatings
have also a worse reflection in the NUV. So its always a
good idea to ask the vendor for details before buying some-
thing.

The SBIG CCD chamber entrance window (should be MgF2
coated BK7) is not as limiting as the Kodak chip sealed MAR
cover glass (Multi AR coated). For U band photometry one
without a cover glass would be advisable.
Other CCD camera vendors than SBIG (like FLI) also sell
Kodak chips without cover slip and lets one the choice
between different materials for the CCD chamber entrance
window.

The Kodak ME chips have a higher QE in the NUV than is
explainable by the microlenses. So there must going on
something like fluorisence and/or a much better UR AV
coating. They ME chip are already nearly sufficient for U
band photometry. Better would be of course an UV AR
coated or Lumogen coated chip (like e2V chips available
via Apogee) but these are not common with amateurs.

Clear skies
 Wolfgang

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



----- Original Message ----- 
From: "David Trowbridge" <David at tinyblue.com>
To: "AAVSO Photometry" <aavso-photometry at mira.aavso.org>
Sent: Monday, June 11, 2007 8:14 PM
Subject: Re: [Aavso-photometry] binning considerations


> Thank you Gary and Arne for your very helpful comments.
> 
> Mike, yes actually I had been looking at the Meade LX200R
> series. I could get a bigger aperture for the same money with
> the Meade. But I thought maybe I could do better CCD photo-
> metry (presently BVR, but extending to U and I filters) and
> possibly infrared photometry (Optek's SSP-4) or spectroscopy
> over a wider range of wavelengths, on a system like the 10"
> Tak Mewlon which has no glass secondary (Only two mirrors
> in the Dall-Kirkham Cassegrain). Do you know anyone with
> experience using the LX200R for photometry? 
> 
> By the way, I'll be mounting the new OTA on my new Paramount
> ME, in parallel with my Tak FSQ. What a treat that mount has
> been! With my old mount, I had to discard maybe 30% of my
> images because of jiggles and shakes, now I can keep nearly
> all the images I take! And no tangled cables anymore. Wow!
> 
> David
> 
> 
> 
> -----Original Message-----
> From: mlfleenor at charter.net [mailto:mlfleenor at charter.net] 
> Sent: Monday, June 11, 2007 7:28 AM
> To: David Trowbridge
> Subject: Re: [Aavso-photometry] binning considerations
> 
> Hi David,
> 
> Sold on those Taks are we?.. I have an FSQ and love it for pretty
> picture imaging but for photometry I have to say that an SCT serves
> the need admirably. Especially considering the new corrected
> LX200R series from Meade I'd be hard pressed to recommend
> anything else-except maybe a large newt.
> 
> You'll probably discover that your seeing numbers will likely improve
> with a bigger scope. Smaller pixels will also let you take advantage
> of good nights. They will not seriously degrade photometry on poor
> nights either. Binning 2x2 works  really well but I'd be cautious of
> 3x3 as a saturated pixel or two can really throw your precision off.
> 
> I use a Meade 14 gps ota with an ST10XME and 2x2 binning running
> with a telescompressor and achieve excellent photometric results.  ( I
> often achieve 1mmag precision working with exoplanet candidates.)
> I highly recommend this camera for photometry although you won't go
> wrong with the ST8 either. You will need to watch for saturation when
> binned. 
> 
> The ST-9 depsite it's hype is better suited for astrometry and SN
> patrols. The fov, lower noise and spectral response make the ST8
> a better choice  for photometry imo.
> 
> Mike
> 
> --
> Mike Fleenor
> Volunteer Observatory
> Knoxville, TN
> www.mikefleenor.com
> 
> 
> 
> ---- David Trowbridge <David at tinyblue.com> wrote: 
>> When doing photometry, is it okay to freely use 2x2 or 3x3 binning to
>> achieve the desired image scale?
>> Where I live, the seeing is generally not better than 2 arcseconds I don't
>> think. 
>> The photometry I've been doing so far has been with an SBIG ST-7E
>> camera on a Takahashi FSQ-106 4" refractor which has been giving
>> me 3.5 arcseconds/pixel at f/5 or 2.2 arcseconds/pixel at f/8. 
>> Now I plan to upgrade to a larger scope for greater light grasp and a
>> new camera for faster download times. I'm considering the Takahashi
>> Mewlon 250 and an ST-8XME camera. Using 1x1 binning this scope
>> would give only 0.62 arcsconds/pixel at f/12 and 0.80 at f/9.2. I think I'll
>> need bigger pixels. 
>> Will it work just fine to use 2x2 or 3x3 binning? Or should I consider an
>> ST-9 instead? 
>> Also, will going to a camera with microlensing have any detrimental
>> effects on photometry measurements?
>> Are there any other issues I should be aware of?
>> 
>> David Trowbridge
>> Tinyblue Observatory
>> Whidbey Island, WA