American Association of Variable Star Observers (AAVSO)
Sun, 04/02/2017 - 02:10


I would like some input and advice on getting into photometry on a very tight budget. I am looking at the Orion StarShoot G3 Deep Space Monochrome Imaging Camera. Is there anyone who has experience with this camera? It would be used with a Sky Watcher 80mm Pro APO with about a 600mm fl. Is this reasonable to consider?



American Association of Variable Star Observers (AAVSO)
It ain't cheap

Your 80 mm scope on a goto mount could make a pretty good visual observing system. Visual variable star observing has a lot of plusses. You can get around the sky much faster with a small scope, binoculars, or DOB, than waiting for motors to slew, centering, solving . You get to enjoy the evening under the stars. You can sort of connect with those worlds out there. You don't need to do all the calibration grunt work that are commonly used to make CCD work more useful. You don't need optical filters. Visual is cheap, some can be done with eyes-only. Folks get quite good at it. You learn the celestial neighborhood. With some safari preparation, you can get readings on 20 variables before your toes freeze or you contract mosquito-born diseases. I find it very pleasurable.

CCD observing is work and a ton of details.

Any camera is useable, but a shutter is sure nice. It is a mechanical thing that costs money to reproduce and last for a  million operations. There are several on-line FOV calculators out there. You can defocus if stars get to small.



American Association of Variable Star Observers (AAVSO)
Importance of Image Scale


The biggest issue, once you have an automated mount, is that CCD will give you an image scale of 2.9 arcsec/pix.  This means that if you live in a typical average environment, with 3 arcsec seeing you are only spreading the FWHM sample across ~ 1 pixel.

A typical overlook by new observers is the failure to examine their potential image scale of their contemplated CCD and telescope setup.

This is easy to do with the free “Ron Wodaski’s CCD calculator.  This comes with a number of preloaded scopes and CCD’s but is easy to manually change any of the specifications.  What you need to know is your scopes diameter and it’s focal ratio; then you need to know the pixel size of the CCD and the array sixe.  Plug these values in and the software will calculate your image scale and FOV with that specific set up.

If the image scale and or FOV are inadequate then the observer can look at either different scopes and or different CCD’s or some combination thereof that will provide a useable image scale + FOV.

From the AAVSO CCD Manual:


When you inspect the image of a star, you will notice that it is made up of a group of pixels, with some brighter ones near the center and some dimmer ones surrounding it. Ideal images of point sources made  by optics have an intensity pattern called an Airy disk. However,

in practice the light from stars (generally considered to be a point source) has to pass through the Earth’s atmosphere which diffuses and expands the pattern. The dot which represents the image of a star on your CCD image is called a seeing disk because the seeing conditions have a profound effect on the intensity of the light. In order to measure the intensity of an image like this when it doesn’t have sharp edges, scientists use  the term, “Full–Width, Half–Maximum” (FWHM). This is defined as the number of pixels that are  filled to one–half the dynamic range between the background and the brightest (fullest) pixel in the star’s image.

In order to get the best results you can out of your photometry, you should strive to

Sample such  that the FWHM of your seeing disk is spread across two to three pixels (2-3). This will help to optimize  the signal–to–noise ratio (SNR) and improve the accuracy of your measurements.

By the way, one way to overcome undersampling is simply to defocus your image; in your contemplated setup, with typical average seeing, you would want to defocus such that your seeing spreads out to about 6 arcsec.  This would give you the 2 pixel sampling objective.  On the other hand if you can locate a CCD with smaller pixels (maybe around 4u) then you will be in a much better sampling situation.

Many CCD imaging programs will measure your FWHM as each image is taken which then can allow you to determine the best defocus point.

I agree with Ray that you mght want to look at visual observing as the best entry point, especially, when considering the costs that will add up for your mount, CCD and then software.  On the other hand, for all I know, you may already be an expierenced visual observer.

Just remmber that there is no such thang as a dumb question and you can get a lot of answers on the forums.  You might also want to consider requesting a mentor for which ever direction you might choose to go:

Ad Astra,

Tim Crawford, CTX

Royal Astronomical Society of Canada (RASC)
Experience with G3 and low-cost(?) setup

Hi Duane,

The G3 is quite feasible to use with a Skywatcher 80ED, but as others above had noted it may not be the best way to start.

I currently use an Orion G3 with a Skywatcher 66ED Equinox with 400 mm focal length on a HEQ5 mount.  Since the pixel size is 8.3x8.6 microns, the CCD is about the same size and sensitivity as an ST-7 or equivalent.  For me, this results in a set-up that is roughly equivalent to one of the Bright Star Monitors albeit with a smaller FOV.  However, the G3, telescope and mount are just the start.  You also need a filter wheel (I use a low-cost Xagyl one), and you probably want photometric filters (I use AstronDon B and V).  In Canada, those items alone added close to $800 on top of the rest.  I used various free-ware software packages for several years, and found I spent a lot of time chasing down or working around their limitations (e.g., image acquisition package that didn't convert to UT correctly, packages that assumed the pixels were square, that rounded off the size of pixels to the nearest micron, etc.).  Recently, I gave up on all of those and bought MaximDL (add another $800 in Canada), and immediately found out why so many people use that package.  I also found that the focal length depends upon the filter (no surprise), but I cannot compensate for that easily. So I finally decided to get an electric focuser (a FeatherTouch so I didn't have to mess around) - another $1600.  I'm happy with the package now, and becoming very productive but no way is it low-cost.

Instead, I agree with the recommendation to start with visual. I still do that a lot with the 66ED as it is so easy to set up anywhere.  I take it tent camping on the road and can observe at anytime.  If you want to dip into photometry, a better place to start for low-cost is with a DSLR.  You can easily get a reasonable APS-format Canon for the same price as a G3, and use the freeware with guidance from the AAVSO DSLR handbook.  You don't need much else after the DSLR.  I started that way during the Eps Aur campaign.



American Association of Variable Star Observers (AAVSO)


Thanks for the replies.

I've been doing visual observing for some time. I've been reporting visual estimates for about 4 years, although my first estimates were of HR DEL in 1967. 

I use the 80mm refractor, 4.5" reflector and 10X50 binoculars. I also have a 12" dob but I'm getting old enough so that it is not so easy to pack it out and set it up. On the two telescopes I use an iOptron ZEQ25 mount.

I am considering building a small run off shed for the mount to save set up time. With that in mind, I thought I might as well look into photometry. I have done the Choice courses VSTAR and VPhot and some reading so that I have a little idea as to what photometry entails. I'm just a little unsure as to whether I can afford to attempt such a project.

Thanks again,


P.S. Tim, you are in Oregon, is that correct? I live in Springfield Oregon, which doesn't have much for an observing season.

American Association of Variable Star Observers (AAVSO)


Sorry for the late reply, I just came across your post as I've been somewhat out of action since April owing to poor health.

What is your budget?

I have a photometer that is an uncooled CMOS camera attached to an electronic filter wheel with BVI filters. The camera is US$599, FW is US$199 and my DIY filters cost me ~ US$150 to make. My magnitude transformation equations are linear from -0.1 < B-V < 1.7 for AAVSO standards in the cluster NGC 3532 and close to zero (within range of -0.1 to 0.1). Color transformations are close to 1 (+/- 0.1). The camera is run using the freeware program SharpCap - a very user-friendly and stable piece of software.

The camera is 12-bit which is the minimum recommended by Howell (2000) for photometry. I reliably measure to an accuracy of 0.02 magnitudes. My setup is easy-to-use. Happy to send you photos and details of equipment, plots of instrumental versus standard values for AAVSO standard stars, transformation equations, and any other details if you wish to email me. My telescope is a cheap Skywatcher 150 mm f/5 Newtonian (~$400) on an EQ6 GOTO mount. I do not use individual exposures greater than 60s and can measure stars down to 12th magnitude. The CMOS camera has much faster download times so shorter exposures can be used, with linearity preserved at exposures as short as 0.5s.

I'm currently experimenting with a 14-bit CMOS camera which should give 1% accuracy. My aim is to develop a photometric system comprising small telescope (70 mm f/7 refractor or 114 mm f/5 reflector, small, portable GOTO mount and color astronomical CMOS camera for ~ US$1000. This could bring photometry into the reach of many more 'citizen scientists'.

I can also help with design of a cheap roll-off roof observatory. Mine is based on a 2 m square garden shed I bought from my local hardware store for < AU$400. Rails and other items bought the total cost up to ~ AU$1000 which is less than my wife's gazebo (AU$1300). The observatory has been up and operating well for 3 years.

Yes, I'm the ultimate cheapskate!


American Association of Variable Star Observers (AAVSO)
Experience with the Orion G3 camera


By the way I successfully used an Orion G3 monochrome camera for photometry for 18 months. I had it coupled to an Orion 7-position Filter Wheel. A low-cost combination that yielded good photometric results. Happy to sent you images, photometric results, transformations, etc.

Unfortunately the Orion Camera Studio software would intermittently crash for no apparent reason. Annoyingly, it would put the date images were processed in the FITS header rather than the mean of when they were captured.

The Orion FW worked well under Windows XP but I had all sorts of trouble getting it to work under Windows 7 even when I downloaded the new drivers. I am a careful person and my camera and FW were left permanently set up. Unfortunately the USB socket of the FW  'disintegrated' and I had to take the FW apart and solder a new one in. I cannot recommend the Orion G3 or FW to you.

Sold the Orion FW and bought a 5-position Xagyl FW. This worked well but at the beginning of this year I sold it and put an extra $20 to the proceeds from its sale to buy the ZWO 5-position EFW! This FW easily connects to and runs automatically from SharpCap once drivers are installed. It will also accommodate thicker 32 mm filter cells and taking off the cover to install the filters is easier. My system is now very reliable and hassle free.


American Association of Variable Star Observers (AAVSO)
starting off right in photometry

Although your question was about camera and telescope compatiblilty (and this is an important question), the most improtant part of a CCD imaging system is the mount.  If you start with a poor mount photometry will be difficult and not much fun.   

Buy the best mount you can afford (even one you can't quite afford), then put together a camera scope system buying used equipment on Astromart or Cloudy Nights. 

For example, Tim Crawford (author of comment #3 in this topic) is selling his ST-9xe for a very attractive price.  Combine this with a used C8 ota (typically about $300 used) and you'd have an excellent  photometry setup for the average amateur's observing site with mediocre seeing.  This would probably cost less then the camera/scope system you originally described, and I think it would be better.  You'll need a filter wheel and filters as well.  (Maybe Tim would make you a good deal on the whole shebang.)

   ...but start with a good mount.



American Association of Variable Star Observers (AAVSO)
lower-cost VRI filters


As you live in the US postage charges for stuff sourced from your local manufacturers are probably not high? If so, you could explore Thorlabs for the glasses to make VRI filters. (There are probably other suppliers, you may want to do a more complete search than I did.)

They sell these in 25.4 mm diameter, 2 mm thickness:

FGL495 (Schott GG495 equivalent) - $35.50 ea.

FGL570 (Schott OG570 equivalent) - $25.50 ea.

FGB39 (Schott BG39 equivalent) - $26.25 ea.

FGS900 (Schott KG3 equivalent) - $36.25 ea.

FGL9 (Schott RG9 equivalent) - $25.50 ea

FGL420 (fill glass for I filter) - $25.50 ea.

Cementing the FGL495 to the FGB39 gives you a V filter and the FGL570+FGS900 gives you an R filter for $61.75 ea. (c.f. commerial ones costing $200 ea.). If you can't find someone to cement the filters for you then with some effort and care you can do it yourself using a cheap cyanoacrylate glue (super glue), see URL: If you mess up the gluing then separate using Methylene Chloride (which is the active ingredient in many paint strippers), wash the components, clean with isopropanol and try again.

To make an Is filter, which can be used in place of an Ic filter for all but those 'studies involving the reddest stars' (see Goldman, Hendon & Schuler's paper at: ) you can use the FGL9 and cement a FGL420 to it as a fill glass. If you are not worried about the I-filter being parfocal with other 2 filters (i.e. don't find a small re-focusing onerous) then you could use a Schott RG9, 3 mm thick filter which is available from Edmund Optics for $41.50.

Mounting 25.4 diameter filters in standard 1.25-inch filter cells made for 28 mm diameter glass can be a challenge but I sourced a cheap 4-piece set of planetary filters on ebay for ~US15. These have the standard 1.25-inch thread for eyepieces and filter wheels but have 25.4 mm diameter glass. Just throw away the glass and use the cells! A VRI filter set will then cost you ~ US$180 + postage charges rather than $600.