Hello:
My name is Paco Santiago, and I’ve been an amateur astronomer since my youth. When I was young, I made observations of eclipsing binary stars, first visually applying the “Argelander degrees” method, and later using a photometer with Johnson filters. I also created my own Photometric Reduction programs, and programs for obtaining light curves, and calculating O-C residuals, etc. Due to serious illness and work-related problems, I had to abandon this hobby for almost 40 years. Now, as I’m getting older and retired, I’ve decided to return to my old passion (which I never forgot), but I’ve run into a serious problem: I’ve become quite outdated. I almost mastered photoelectric photometry with a traditional photomultiplier. Nowadays, CCD and CMOS sensors are used. My lack of knowledge of this technology is complete, and I’m trying to update myself to resume my old hobby. Although I have a Meade SC (an LX 50), I now want to buy a small piece of “field equipment,” one that is portable and that will allow me to travel to places without too much stray light, where I can make my observations. I’ve thought about buying an equatorial mount with GoTo (EQ 5 or perhaps EQ 6), with a Newtonian-type optical tube at f/4 and 20 cm in diameter, with tracking done with autoguiding, that is, with a small guiding camera and a small refractor. So far, so good, but I’m running into the serious problem that telescope stores only advertise CMOS cameras geared toward astronomical photography, but without specifying whether or not they are suitable for photometry. I’m clear that the camera must be monochrome, that it must be cooled, and if possible, that the ADC be 14 or 16 bits. On the other hand, as a retiree, my budget is quite limited, and the price of the camera should not be higher than $1,500. Can any AAVSO members with experience in this area advise me on some camera types I could use?
Note: I have a set of two Johnson BV filters.
Hello Paco, glad you are getting back into a hobby you are passionate about!
I have several ZWO CMOS cameras that have performed well for my needs. They have somewhat recently come out with the 2600MM Pro Duo, which has a separate, integrated guide camera. I bought one but haven’t had a chance to really test it out yet.
It is a little over your price limit, but since it has a guide camera integrated, it could eliminate the need for the additional scope and camera for tracking, which could actually save you money.
I think most modern CMOS cameras are pretty good, especially since you already know you need one that is cooled and monochrome. So you should have lots of options to suit your needs and be within your price limit.
You’ll have to keep us updated with your progress, and obviously ask any other questions you may have!
-Kenneth
Thank you very much for your response, Mr. Kenneth. I’ll try to buy what you recommend, but first, according to what I’ve read, the optics of the telescope used (primary lens diameter, f/D ratio) determine, to a certain extent, the size of the sensor pixels. You also have to calculate the FOV and the resolution in arcseconds per pixel, etc. And as I’ve explained before, I’m a complete idiot when it comes to CCDs. I hope that when I’m better educated on this subject, I can decide what equipment to buy. I just wanted to know if monochrome CMOS cameras priced around $1,000-$1,500 were suitable for photometry. Anyway, thank you very much for your response.
P. Santiago
Hello Paco,
Yes, I think modern CMOS cameras are excellent and work well for photometry. And there are good options in that price range.
I like using this webpage when deciding on telescope and camera combinations:
It will calculate many of the things you mentioned, and the reference (Sun, Moon, Jupiter, etc) helps me quickly get a feel for the image size.
The pixel sizes of some CMOS cameras can give pretty small on-sky sizes, which depending on your local average seeing can be good or bad.
-Kenneth
Forget EQ5-6 for mobile device!!! There are excellent “harmonics” mounts with wave reducers - they are more lighter and precige of old good German ones.
Mikhail, owner of black HEQ-5.
Good point on the mount! I guess I just skipped over that.
I don’t have one yet, but the strain wave mounts are supposed to be excellent - good tracking and light weight.
-Kenneth
A number of people in AAVSO are using a 533 monochrome camera. I use the QHY 533M ( a cooled camera) and have been quite happy with it. I imagine another brand with a 533 sensor would perform as well. Pixel are 3.76 microns and it has a a good well depth which is important for photometry. I would also second looking at the Astronomy Tools website to see what combinations of different scopes and cameras will do. Its almost a try before you buy.
The mount is crucial. I have an HEQ5 Pro and an EQ6R and I have done photometry with both, but I have a small permanent observatory to house the EQ6R. The HEQ5 was a challenge to set up every time but doable. I would not be using the EQ6R as a portable unit as it is quite heavy. The strainwave mounts would be the way to go,as they are much lighter and can guide fairly well.
It is good to see you on the group Paco. Welcome.
Your original question was about using a CMOS camera. I wouldn’t have any reservation about using a CMOS camera for photometry. They are much improved from what you will read about in the literature. I do think most professional observatories use CCD sensors, but many of us hove used CMOS sensors with excellent results.
Personally I use the ZWO ASI183MM Pro cooled monochrome camera. First it’s limitations: It has a 12 bit ADC and suffers from amp glow on the side of the image that visibly extends to near the center. The amp glow is very stable and in my experience is removed from the calibrated images. Look at the QHY website and you will see a comparison of the 183 versus 533 dark image. I think the photos that QHY shows are a good representation of what I experience.
The advantage I see is that the smaller 2.4 micro pixels of the 183 are a good match to my seeing conditions. You should calculate the arcseconds per pixel you expect with your telescope and consider the combination of various sensors.
If I were buying today, I’m not actually sure which I would choose.
If you decide you are happy with the 3.76 micron pixels of the 533, I do actually think the DUO sensor with integrated guide sensor would be worth looking at.
I wish you the best, and again, welcome to the group.
Clear skies,
John
First of all, thank you very much to all of you who have advised me. Now that I know a little more about the theoretical aspects of CMOS cameras, I’m absolutely certain I’ll buy a monochrome one, and possibly the V filter. I had two filters, B and V, but the V filter deteriorated before I even used it. I’ll probably also buy the U filter, since I’ll now be using a Newtonian instead of an old Cassegrain (Meade LX 50), where I couldn’t use the U filter because of the correction lenses. As I said in my previous post, it’s been practically 30 years since I last used my old equipment, and I’m afraid it’s deteriorating. I will only be able to reuse filter B, an Atik filter wheel, and possibly a focal reducer in case binning is necessary. (It is curious that about 15 years ago I wanted to resume my hobby, and I bought an Atik 16IC CCD camera, with which I hoped to get started in photometry, but again a fatal illness forced me to retire, and today it has not been used even once …). By the way, looking at monochrome cameras with an IMX 533 chip, the one that attracts me the most is the OMEGON veTEC 533. What do you think about this brand? I am still completely ignorant of this subject. Thank you very much to all for your collaboration, and sorry for my bad English. I use Google translate. Greetings from Sierra Nevada in Granada (Spain).
Regarding filters, you may want to consider the CBB for photometry if the color of the target is not of particular concern. Bruce Gary and I wrote a little summary of the CBB here: https://cbbldc.com/CBB%20Filter%20Advantages.pdf
As far as cameras go, depending on your budget, you might want to look at the FLI KL400BI. I have always liked the camera for the unusually large pixel size of the GSENSE400 sensor. The description of the camera is here: KL400BI | Scientific Camera by FLI
Ed
Hi Paco,
What about buying a smartscope? For instance, Dwarf 3 is not best for photometry, but somewhat acceptable (an RSME of 0,2 mags when comparing Vmag with its green channel). Setup is super easy and fast, it’s very portable and has a large FoV (around 2 degrees). Magnitude range goes from 5 to 15, depending on the exposure time. Also, it delivers very good pics if you want to do some astrophotography.
The obvious advantage of smartscope (or DSLR) is possibility to get TB, TG and TR images simultaneously. The no less obvious disadvantage is impossibility to use standard filters.
I myself use uncooled mono camera with RGB photo filters, so I do not have the advantage 
However my modest experience shows possibility to get comparely reliable photometry with stacking of tens of short exposure (3-8 sec) images, so smartscope maybe reasonable choise, especially for mobile device.
Hi Paco,
I’m using a Seestar S50 automated telescope to observe AAVSO legacy eclipsing binary variables. It’s well within the $1500 budget and is very easy to use. Just take it outside, put it on a solid surface, enter the object’s coordinates, and away you go.
Seestar S50 uses its built-in color RGB camera, but that’s not a problem if one of your interests is to time the minima of eclipsing binaries. Afterwards, I use Pixinsight software to extract the Green (TG) data and then do photometry using the free Lesve Photometry program. By the way, AAVSO accepts data taken using the TB, TG, and TR filters that are common on CMOS color cameras.
I’m retired like you are. The Seestar S50 works perfectly for almost anything I want to do, including variable stars as faint as magnitude 14 or 15 using Seestar’s track & stack integrations.
Thank you, Andy, would you please inform typical total exposures for 14-15m stars, catched with Seestar?
It depends on sky brightness (Bortle number) and desired precision. About 5 minutes should work in most cases for these fainter objects. However, Seestar stacks only the best frames. So, the total time elapsed may be more like 10 minutes. For the legacy EB stars, I typically use 10 second integrations, which are precise to about +/- 0.1 mag for stars in the range mag 9-12.
The Seestar S50 has 50mm f/5 optics (i.e., focal length 250mm). 14th to 15th mag stars imaged with this equipment should only be measured, in my opinion, if you stacked many exposures first. I don’t believe that short period variables with periods of only a few hours would be appropriate targets if the aim was to obtain accurate light curves of the mid eclipse (edited).
Hello Paco,
Your story is uncannily similar to mine with an enforced break after 10 years of PEP and a return at the grand age of 68yrs in 2023. I had given up hope of a return but I was advised that the tech had moved on and I could conduct CMOS photometry from indoors with the AISair system. I have asthma and can no longer be exposed to the sustained cold.
My complete optical system is:
Sharpstar Carbon fibre 90mm triplet refractor FL 600mm
ZWO – AISI 1600MM Pro mono camera - cooled
FOV 1.69 x 1.28 deg
Image area 17.6mm x 13.3mm
Baader Bessel Photometric B&V filters.
ZWO ASIAIR Plus
12 bit with 2^12 = 4096 different
As you can see it’s not a particularly high spec or large scope but works very well. With photometry
down to about 14 mag in B&V.
The ZWO ASIAIR Plus is a self contained mini computer with wi-fi which sits on the scope and controls EVERYTHING (via a phone or tablet) including the mount which is a Skywatcher EQ R Pro, the ZWO filter wheel and focusser.
I have a ZWO guide scope but have never needed to use it as my exposures are always less than 60s.
The EQ6 R Pro mount copes easily with the combined weight of my set-up but is definitely not portable and others can advise you better on suitable mounts. The GOTO function improves efficiency if you are moving around the sky a lot like I am, but may be less important for EBs.
I am not very technical and had much help with the hardware from local astronomers who were imagers as they have a similar set-up albeit colour cameras.
Then I had to take those raw images and learn how to calibrate, stack and conduct photometry on them.
I found ASTAP the most user friendly stacking calibration software(and it’s free) and the AAVSO’s VPHOT online system for photometry of calibrated images. AAVSO members have also been a great help with my stupid questions on these forums. I can talk you through each stage if it helps, or just fire away with questions.
Regards
Kevin
Hi Paco:
I use a SeeStar S50. I have been using it for astrophotography and variable star observing. I live in a Bortle 7 region. There are several advantages using the SeeStar, if you save all the raw frames. This allows you to stack several to get a time series. You can capture all three colors at once, without the need of a series of filters. The TG channel closely matches the V filter. The other colors, they do not match as well. However, after going through an exercise with calculating transformation coefficients, the errors among all the colors have been substantially reduced.
Another thing about smart telescopes, is the ability to set up a plan, and have the telescope execute the plan. For instance, tonight I am doing a plan 9 variables. Five of those are short period variables less than 90 minutes each, and four are long period variables where I image for 30 minutes each. I tend to focus on variables less than a minimum magnitude of 12 or so to enable me to get a decent SNR and a decent light curve. For the fainter long period variables, I will use something like a 9-10 minute exposure (27-30 frames of 20 second exposures) in an equatorial mode. Sometimes, I will also go up to 15 minute exposures. I am typically limited to a magnitude of 14.5 to 15 because of my heavily light polluted skies.
I like the SeeStar because it is easy to use, portable and light weight (3Kg). I can just put it on a tripod and use it in the alt-az mode, or I can take a bit of extra time (10-15 minutes) and set it on a wedge, and polar align it.
As for the results of photometry, here is some results that I was able to achieve one night on AE UMa:
Like you I am retired. I tried doing visual observing when I was a teen ager of variable stars, but for a variety of reasons, I was not able to get satisfactory results. With the SeeStar, I have been able to accomplish that goal, while also learning astophotography. I have been able to accomplish more with the little SeeStar S50 than I was ever able to achieve using a much bigger telescope. The cost of the SeeStar was about $500 US, so well within your desired budget.
Scott (MDSA)
Collegeville PA
You can also save the raw images, so that you can group them in stacks of different expose lengths. For instance, for brighter short period HADS, I would typically use stacks of 12 or so, 20 second exposures, to achieve the desired SNR. I use ASTAP for stacking in groups, and for data analysis.
I would not use the stacked FIT file from the SeeStar, as the software likely has done some processing to the FIT. I would only use the raw images and stack those in groups using your favorite software.