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Recommendations for camera for variables

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SVD
Recommendations for camera for variables

I am looking at buying a camera for variable star photometry.

Don’t care about pixel size, sensitivity, and those other considerations. I have plenty of telescopes and mounts that cover those considerations.

What I want to know is the camera YOU would recommend.

Eric Dose
Eric Dose's picture
There's no answer to your question as posed.

To do what you want, you must care about pixel size, sensitivity, etc so that you can reasonably match the camera to the telescope for a given observing aim. And there exist very different aims all within variable-star photometry, including long-period variables, very fast-cadence cataclysmics, or might be very red, very faint, or very bright. The available filter wheels and guiding will influence camera choice. People have different cameras for good reasons.

So there's no answer to your question as posed. It's like asking what house we would recommend without knowing a thing about your family size, budget size, or preferences for weather, urban/rural life etc.

Knowing a bit about what you're trying to measure and what equipment you want to match this camera to--that would help.

hambsch
hambsch's picture
CCD Camera

As Eric mentioned that it is difficult to answer your question.

If you have the budget I would go for a FLI CCD with a big chip, maybe even the new CMOS type FLI's although you might need to cope still with some issues.

I have a FLI ML16803 with 7 position filter wheel and am very happy about the reliability of the system.

I use it nightly from my remote site in Chile.

I observe a multitude of objects all of those Eric mentions and adjust th exposure and filter accordingly.

If you have more specific questions fel free to ask.

Josch

MMU
MMU's picture
Followup on KAF-16803 cameras

Josch's note says:

I have a FLI ML16803 with 7 position filter wheel and am very happy about the reliability of the system.

I'm also starting to look at cameras - something to replace my trusty old SBIG ST-9E (parallel port) camera - and I've created two sensor lists, labeled Naughty and Nice. Pixel size and field of view have strongly influenced which sensors go on which list, but I had put the KAF-16803 on the Naughty list because of its susceptibility to Residual Bulk Image (RBI). Maybe I've been too quick to do that? (I work with mostly Mira LPV's in BVRI, and I'm frequently battling the limits of linearity/saturation  with my red & IR exposures.) Are any special techniques needed for successful photometry with sensors susceptible to RBI? Does NIR pre-flash make this a non-issue for good photometry?

- Mark

SVD
Thanks for the replies.

Thanks for the replies.

BUT the question I am asking is the better camera’s for variable stars. Right now, it seems that linear response is the MOST important factor.  Is that correct?? And which camera’s have the best linear response?? Does anybody know??

Look at the problem from the perspective of holding ALL OTHER variables constant from the analytical perspective and just focus on the camera.

For example, it appears that there are many issues with CMOS camera’s. Does that mean that CCD camera’s are preferred??

I guess, I am at the point in my life where I am tired of “kludge” solutions.  I did enough of those while working and this is a hobby not a profession.

 

spp
spp's picture
Answers

Right now, it seems that linear response is the MOST important factor.  Is that correct??

No.

And which camera’s have the best linear response?? Does anybody know??

No.  All CCD cameras have a linear response up to a point.  The important question is how do we know what that point is, and how do we avoid going non-linear in our observations.  You can do good photometry with almost any CCD camera if you know what you're doing. 

For example, it appears that there are many issues with CMOS camera’s. Does that mean that CCD camera’s are preferred??

IMO, yes.  CMOS is the future, but this is now.

I guess, I am at the point in my life where I am tired of “kludge” solutions.

If you continue to focus your decision making only on the camera you are almost guaranteed eventually to end up kludging something together that is less than optimal.

...more answers below.

SVD
Hambsch....thanks for your

Hambsch....thanks for your comments. I looked up your camera and it is outside my price range.

Maybe I should rephrase the question....” what are the best CHIPS for variable star monitoring??

spp
spp's picture
Questions

Ken gave you a good answer to your specific question about CCD chips, but I think you are missing the bigger point that everyone has been trying to convey.

THERE IS NO BEST CAMERA.  THERE ARE NO BEST CHIPS FOR ALL SITUATIONS. 

It depends on your site, your budget, what you plan to observe, and what components you already have.  Please understand that we all want to see you get the best system consistent with these conditions.

Here are some of the questions I think you should be asking:

How do I select a camera/telescope system that is consistent with my seeing?

What is the most common mistake made when selecting a camera for photometry?

What is the single most important component of a CCD photometry system?  (Consider system to include telescope, camera, mount, filters, software, enclosure.) 

I'm sure Eric, Josch, and Ken could suggest a few more.  Much of this is covered in the AAVSO CCD Photometry Guide. After all these have been discussed would be the time to start talking about specific cameras and chips.

Phil

 

 

MZK
MZK's picture
Criteria?

Vladimir:

If you have a common restriction such as price, why not just state what it is? This will save a lot of time.

BUT If you insist, IMHO, 16 bit CCD, NABG, 100,000 e- full well, back-lit ($$$) for high QE or front lit ($$), FOV about 30 arcmin in your scope (?). You do not need the biggest chip! Look at 6303 chip specs as a start.

BUT, new CMOS cameras ($) can work with some understanding of their bit depth and well depth restriction, etc.

Ken

hambsch
hambsch's picture
My CCD not optimized

Hi again,

my CCD is definitely not optimized for the scope I use. I have a FL of 2.7m and my CCD has 16 Mpixel of 9x9 microns^2. An image of 1x1 bin is 32 MB. I get about 800 images a night and observe 320 nights on average. Hence in full resolution it would be hard to get all this stored and transfered from my remote site:

I generally bin 3x3 to reduce file size, but my photometry does not suffer from this. As said I observe all kinds of objects close to noise level (mag 19 or so) and close to saturation level (mag 8 or so).

I do not think you will find an optimal solution if you only go for the chip. All CCDs and many of the modern CMOS (e.g. ZWO1600MM Pro or so) can give you very good photometry. I am approaching the problem from the pragmatic side. You should use what you already have either DSLR, CMOS or CCD and see whether you can do what you want to do. You need to look at all components not only the camera, but the mount and scope as well. Also your possibilities in terms of observing cadence, weather, permanent setup etc.

I would recommend just use what you have or if you do not have a camera yet, go for a 2nd hand either monochrome CCD or CMOS and give it a try. If it does not suit you you did not invest too much and can sell it again.

I bought my CCD (ML16803) also in view of a possible selling in a few years to somebody not interested in photometry but astrophotography.

Concerning RBI, indeed there is a small problem, but it mainly depends on the brightness of the object. For MIRAs some could be very bright and then you need to go for a different scope to go for those.

You can look at my observations of Miras like U Ori, wehich goes from mag 6 to 14 or so depending on the filter. I have a 40 cm scope and you can see that maybe oinly the brightes points in V have scatter which is due to saturation. This is an example of a very bright object with a very big scope. I should remove those data.In B however it seems to be fine. Anyway if you see the smoothness of the curve you can definitely not say that RBI is a problem. Those images are taken during a session run every night amongst 800 others.

Josch

SVD
Thanks for the comments and I

Thanks for the comments and I am looking forward to more....

Equipment:

I have about 10 scopes ranging from a 12.5 f5 newt to a Orion 80 ED.

I have three equatorial mounts: A AP900, a Atlas EG-G, and a Celestron AVX.

I have the following camera's: SBIG ST7 XME, SBIG ST-I, and a Canon 6d camera.

I have three sites for observing: My house in Wenatchee, basically living at the bottom of a waterfall when it comes to air flow. Mountains are 8000 feet less than 10 miles from town at 800 feet. Second site is 10 miles west of Wenatchee at 3000 feet, the seeing is much better. The final site is 2500 miles south of Wenatchee in Arizona. It is real stable.

The Wenatchee site has an roll-off roof observatory. The Cascade site has a observing platform and I can put a structure on it. The Arizona site is a lot, but I cannot put a observatory on it. Wenatchee is 20.4, Cascade site is 21.6 and Arizona is 20.9 at zenith according to SQ-M readings.

I do have price constraints. Would like to stay under $2000 US$.

Right now I am focusing on using the ST-7XME for variables, but I would like to be able to buy my NEXT camera if I see a good bargain on one.

Oh, astronomy is one hobby. There are others that take up spring and fall in particular. Winter and summer are probably my primary times for astronomy.

That is one reason for wanting something that works....since astronomy is not my only hobby I really don't want to "kludge" things to make it work.

Does this help in understanding why I would like a simple answer?? Yeah, I know I have too many hobbies....that is the primary reason I retired early from a perfect job.

Oh, I really don't care about a camera to take "pretty pictures".

spp
spp's picture
ST 7

Thanks for providing the information.

I agree with Ken, use the ST7.  The KAF 0402XME chip is very good for photometry.

If you used your ST7 with a 0.5X focal reducer on a scope with a 2000mm FL (i.e. a standard C8 or M8) you should have an image scale of about  ~1.8 arcs/pixel ( good for most amateur sites) and a FOV of about 23 X 15 arcmin.

If you're itching to get a camera with a bigger chip on a $2000 budget I'd suggest keeping your eye on Astromart and Cloudynights looking for an ST-8XE, or better, an ST-8XME.  I also think the ST-9XE and ST-9XME (20 micron pixels, 512 square) are excellent for scopes with a FL 2m or more, but they are rarely seen for sale.   

I think all of the chips used in the ST7 series, 7, 8, 9, 10, especially the "M" versions with the microlens, are good for photometry.  Some are available with anti-blooming, so I'd check with the seller about that.  You can do good photometry with an ABG camera, but NABG would be preferable.  If you buy one of these used on line they often come with a filter wheel still within your price range (or you could use the FW from your ST7).  All the CCD's in these cameras (KAF 0402E, KAF1602E, KAF1602E, KAF 3200E) use the same technology, but with different numbers of pixels and size of pixels.

Yes, there are good chips in higher tech cameras, but within the $2000 budget I think one of the ST7 series, bought used on line, would be your best choice.   (...and you already have one.) 

Do you know what your seeing is in Wenatchee (arcs/FWHM)?  Ideally, you want to have a camera and scope combination that gives (or can be made to give using a FR or binning) 2-3 pixels across the FWHM of your typical seeing.  This is covered in pages 17-20 of the CCD Photometry Guide.     The  SBIG FR237 works well with my ST-402ME camera.  ...same CCD chip as your ST7.

If you needed a FR for one of the larger ST 8,9,10 cameras, the FR237 would probably be too small.  You would need a larger FR.  Optec makes the ~2 inch size "NextGen" 0.5X and 0.7X FR's that would probably work well with the larger chips.  I think there are other sources as well.

Again. I'd recommend just starting with your ST7.  Use one of your scopes (and FR or binning if needed) that gives approximately the right sampling for your typical seeing.  If you don't know your typical seeing, ask someone who is doing astrophotography, or measure it yourself using the ST7.  Instruction are in the CCD Photometry Guide.

I would recommend against getting a CMOS camera now for photometry, especially for a beginner.  The prices are very seductive, but you'd have to find someone who can explain how to use it for photometry.  Someday, soon I hope, there will be some document or CMOS Photometry Guide to do this.  We're not there yet.

Observing site: At least for starters I'd put it in the roll-off near your house, even if the conditions there are not as good as in your other sites

Phil

MZK
MZK's picture
Stick with what you have

Vladimir:

Your ST7-XME is a very nice camera!  It certainly cost more than $2K? I've had mine for more than 10 years. It meets all my recommended criteria. Don't buy a new camera until you need one, i.e., when the ST7 fails. If you only do photomertry part time (not every clear night), why buy another camera? When you do need another, buy the best you can afford, e.g., something similar to the ST7 when you first bought it?.

A quick search on OPT will show you that better ccd cameras cost more than $2000, and you should have a filter wheel too!

IF you are chomping at the bit and must buy another camera, IMHO, consider one of the ZWO CMOS cameras (e.g., ASI 183) with a filter wheel and BVI filter. You can do much of this for $2K. They will become more mainstream for amateur photometry.in this price range. A very good CCD is tough to get at this price except if used.

Ken

 

SVD
Thanks for the comments.

Thanks for the comments.

I am going to go ahead and set up my 8 SCT  with a focal reducer on the AP Mount for variables. It is in a roll-off observatory. I will go ahead with using the ST-7.

I was in Starzonia in Tucson and saw the new ZWO camera’s and their small size relative to the ST-7. That  got me thinking about a new camera.

Thanks, everybody.

spp
spp's picture
New photometry setup

That sounds like a  good combination.  You should be able to have a lot of fun doing CCD photometry with that system.  

Phil

MZK
MZK's picture
Perfect system?

Hi Vladimir:

I think you made a great decision for several reasons:

1. You avoided the astronomer's affliction - buying new observing toys because your money was burning a hole in your pocket!  ;-)

2. You will use your backyard observatory so there is less reason to avoid observing every clear night since you only have to walk for 1 minute.

3. Your MOST important choice is selecting the AP mount. A high quality mount is the key component to easy/efficient photometry. The scope and camera are secondary.

4. The focal reducer will give you an acceptable FOV (15 x 20 arcmin?). Make sure you select the FR based on whether you have a new (ACF/HD?) vs old SCT.

5. IF you still want to spend some $$, I recommend that you invest in an ethernet cable to the observatory so you can run from the comfort of your house.

6. Buy observatory control software (e.g., CCDAP, SGP, ACP, Maxim?).

7. THEN, you can run the system while you are asleep and have no excuse not to continue your other hobbies AND astronomy!  laugh

8. IF SO, you will become addicted to photometry!  ;-)

Ken

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