Hi all,
I currently have a loan SBIG ST-7E. I am looking owning my own camera and the primary functions will be BVRI photometry and spectroscopy with an SA200. The two cameras I might potentially purchase at this stage are an SBIG ST2000 and an SBIG ST-7XME.
The main issue I have with the loan ST-7E is the small FOV. I compensate with an Optec NextGEN 0.5x focal reducer. This risks undersampling. To avoid that I can defocus slightly if the field allows at the expense of light intensity.
The SBIG ST2000 is a roughly 2Mpx monochrome device. It will solve the undersampling issue and offer a larger field of view than the ST-7 models. However, it's QE is not as good as the ST-7E or the ST-7XME. It would also appear to be lacking in response at the red/infrared end. Peak QE of the ST-7XME is 85%, peak QE of the ST2000 is around 55%. I will correspondingly have to make longer exposures with the ST2000 - noise depending.
So this is a tale of trade offs if I make any purchase at all.
I would appreciate any input from anyone using or familiar with either camera or who can speak more authoritively to the issues/trade offs I need to consider.
Thanks!
- Carl Knight.
Carl
You need to factor in the fact that the 2000 is an antiblooming only camera. You also need to make sure that the ST7 is non-antiblooming. I think the ST7 comes both ways.
Gary
Yep. The point being
Hi Gary,
Yep. The point being I'd have to take care to establish linearity failure and be careful to remain within that because the anti-blooming is going to alter the pixel value. Also impacts the efficiency of the CCD right?
- Carl.
Hello Carl
Yes, that is exactly what you have to do.
Gary
Hi Carl:
You appear to know the pros and cons of the ccd options. Have you tried the options in the CCD Calculator to see their impact?
I personally think that the sweet spot in terms of FOV is about 30 minutes (at least about 20 min). A large well depth (e.g., 100,000 e) is ideal but most observers work with less. NABG is also better but you can cope with ABG. Your scope is not really going to achieve this unless you use the 0.5 reducer. You also want to match the pixel size with the image scale of your scope to yield FWHM of about 2 pixels (w/binning).
Have you considered an 8300 chip? Also ABG but it can work with the care you mentioned. Would work at f/10 with binning. Look at the Stt 1603 and 3200 also.
Unfortunately there is no perfect answer or choice. $$ does play a part.
Ken
Hi Ken,
Regarding the ST-7... My FOV with the 0.5 FR is 15.6' x 10.4', on the diagonal, 18.75'. Without the 0.5 FR it is naturally enough 7.8' x 5.2' and the diagonal is 9.37'.
1x1 binning, 0.5 FR yields 1.22"/pixel. Without the 0.5 FR its 0.61"/pixel. 2x2 binning with the 0.5 FR yields 2.44"/pixel and without yields 1.22"/pixel.
Seeing in my location given the roaring 40s is something like 3" once in a blue moon and more likely 4"+. Ironically in winter some of the best transparancy is accompanied by the worst seeing.
An ST-8XME, with the bigger chip size yields the same arcsec/pixel values, but has covers four times the area of sky in each combination of FR/no FR.
I had a quick look at the KAF8300 chip specs... I'll do the same with the others you suggested.
Thanks,
- Carl.
Another useful piece of info would be the scope focal length / size? I don't think you mentioned it. I use an ST7XME which is a reliable workhorsse on my SN8 f/4.
Ken
12" F10 SCT. And both
Hi Ken,
12" F10 SCT. And both with and without the 0.5 focal reducer.
Thanks.
- Carl.
Hi all,
I did not find this the first time, but this thread pretty much nails the issues:
http://www.aavso.org/choice-cameras-beginner-photometry
For now I can live with the ST-7E. The ST2000 would appear to suffer from:
The ST-7XME is a better camera and unlike the ST-7E has a faster USB interface instead of the old parallel port, but I think I'd be better still finding a second hand non-antiblooming USB ST-8/10. Only issue there seems to be that no one wants to give up their old ST-8/10s!
Thanks for everyone's time and responses.
- Carl.
To: Carl or anyone else,
There is an ST-8XME and CFW-10 (10-slot filter wheel) on astromart now:
http://www.astromart.com/classifieds/details.asp?classified_id=886340
James
There is a used SBIG ST-10XME with CFW-10 and AO for sale on Astromart: http://www.astromart.com/classifieds/details.asp?classified_id=888113
James
I have a ST-7E and an ST-2000. All the issues mentioned above are spot on. the anti blooming feature is a factor. I have lost several good runs due to over exposure so you have to be real careful. My st-2000 goes non-linear above 55,000 ADU's.
Another positive is the low noise of the ST-2000. In fact I have cranked the cooling down to -25C and not seen much difference in noise from -5. This helps in the high desert where I live, especially in the summer time. The ST-7 really needs temps below -10 and even better to >-15. This can be accomplished with a water pump but it is kind of a hassle. In Southern New Mexico where I used to live it would take a bag of ice in an ice chest to get the camera down to -10. Buying bags of ice gets old fast. I actually thought about getting a small ice machine! Not a factor with the ST-2000.
The ST-7 does great on the red to near infrared. ST-2000 not so much. However I like the larger format chip of the 2000 so I just shoot a few seconds longer. Over all I am pleased with both cameras. Each has benefits that you can use and negatives you can compensate for. My ST-2000 came with my 11" CPC so I have just learned to use it effectively. If I had to purchse one I would go with the ST-7XM or even better a ST-8 or 10.
I have an ST-8XE and ST-10XME. Although both are similar in physical width (ST8: 13.8 x 9.2 mm, ST10: 14.9 x 10 mm) I prefer the ST-10XME because, pixel-to-pixel seems more sensitive than the ST-8XE without the microlens. Its good to have both, incase one is down or your shooting concurrently through two different scopes.
Another item to consider is whether the CCD has an option to support an external guide head which the newer ST-8/10's support. Using this "RGH" enables use of an off-axis guider, ahead of the filter wheel. Also, if your using multiple instruments, like a smaller refractor to shoot bright Miras, you can attach this RGH to a small lens and use as a guide scope. They are very sensitive, being cooled, and have an in-built shutter. Of course you can get a seperate, cheaper guide camera, but then you need to add a seperate data cable to your computer and perhaps and extra power supple cable. With the SBIG RGH, it requires a short 3' cable directly to the ST-8/10. I'm on the look-out for another RGH because of their versitility and sensistivity.
I usually see 1 or 2 older SBIG cameras on Astromart every few weeks. I bought all my older SBIG equipment this way and saved probably 50-85% on newer SBIG cameras. What I like about the older SBIG's is that you can add items to increase their function/flexability; i.e. RGHs, 10-filter wheels, 100mm lens, AO, etc.....
James
Los Angeles, CA
May I add another camera choice to those already mentioned?
For years, I have used the ST9xme with Meade LX200 12". 10" and 8" scopes at f/10. The 20u pixel size is a perfect match for these scopes. The FOV is larger than the ST7 and almost as large as the ST8. And those 20u pixels allow for greater sensitivity resulting in shorter integration times and better imaging of dimmer targets.
Cheers,
Keith