[Aavso-photometry] DSI Pro2

[Jeff Hopkins]

Hello Keith,

I do BVRI photometry with a cooled DSI Pro (not the DSI Pro II). It 
works very well. Most of my work is done with 13th magnitude and 
brighter stars. Part of the reason is I live in a very light polluted 
area where seeing a 3rd magnitude star on a dark clear night is rare. 
Even through the main optics of my 12" LX200GPS I see no stars 
fainter than around 10th magnitude. Using the DSI Pro, 11 magnitude 
stars pop out on the screen with less than 1 second exposures. I have 
seen 16th magnitude V stars in images of 30 seconds.

As for the B filter, some stars are much brighter in the shorter 
wavelengths and some in the longer. It depends on what you want to 
observe. Having the B filter is important because you need B and V 
data to calibrate your system.

Save your money and invest in a filter wheel.

I suggest staying away from the fainter stars as there are many 
problems aside from magnitude and blue sensitivity. Finding the 
stars, identifying them, find comparison star that are suitable and 
have BVRI values are all a very big challenge. The S/N of those stars 
will be poor too, particularly with an 8" scope.

I suggest getting the B and R and even perhaps the I filters and a 
filter wheel. Life will be much easier with the filter wheel.

Good luck with your projects.

Jeff



At 11:53 -0700 07/22/2007, Keith Robinson wrote:
>Hi All and warm greetings from Lancaster U.K.
>
>My wife and I bought a DSI Pro 2 last year from someone who was 
>selling them on Ebay - we paid 400 U.K. pounds (about 800 dollars) 
>for the camera plus RGB filter set. My wife who is Secretary of of 
>our local astronomy club wanted to do the pretty picture thing while 
>I want to do photometry. So I also bought a Schuler V filter.
>
>I've found by doing trial exposrues on open clisters - eg M34 that I 
>can easily reach mag16 with a few stakced 15 second exposures and 
>overall my wife and I are very well pleased with it.
>
>I would like  buy a B and an R filter, however a local amateur 
>astronomer friend would does some photometry with an SBig camera 
>fairly winced at the mention of using a B filter and reckoned that 
>exposures would need to be very long to get to decently low mags. I 
>see that Arne Hendon in his article mentions the camera's excellent 
>blue response - does aynone have experience as to what mags can be 
>reached with a B filter and realistic exposures? I'm using the 
>camera with an 8inch f6 Newtonian by the way.
>
>A final 'by the way' is that with a bit of cardboard engineering and 
>some brown parcel tape, I made a couple of covers which slide over 
>the exposed filters  and certainly eliminate dewing problems.
>
>Many thanks and clear skies - we aint had many of those here in the 
>U.K. lately.
>
>Keith Robinson

-- 
Jeff Hopkins
HPO SOFT
Counting Photons
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Hopkins Phoenix Observatory
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