Affiliation
American Association of Variable Star Observers (AAVSO)
Wed, 06/06/2012 - 14:25
Hi Forum.
I have followed the CitizenSky program ( e Aurigae) and learned a lot during the program.
But the program is kind of messy with a lot of good info at not so easy to find places.
There really should be some kind of follow/kleen up on that program so newcommers dont
have give up at first sight.
Great job to all of those involved...but way leave it in a mess ?
Pierre from sweden
Hi, Pierre.
We do plan to migrate the DSLR tutorial and program to the AAVSO. We have a funding proposal pending to help fund a major, printed-or-digital manual for how to do DSLR photometry. This manual will include professional layout graphics, etc. If it is not funded, we still plan to move the tutorial to the AAVSO but it will take longer. Brian, our resident DSLR expert, is leaving for Germany in the summer so is not as accessible as before. We'll need to recruit some more expert advisors to help out. And I'm leaving the AAVSO as well so someone else at HQ will have to take up the banner. It will get done, though. We've ID'd DSLR photometry as one of the key new technologies and areas of growth for the AAVSO.
Hello!
I'm a CCD user. Have been for years. First an ST8 now an ST10. Should I intepret the comment "key new technologies" as the CCD technology becoming a "fringe old technology"? I feel like i've had my head down and now looked up to find the parade has moved on! I've been saving money planning to buy a new expensive new CCD camera with better sensativity in the Blue and UV bands. Our there DSLR's that will out perform my ST10? Certainly the last I looked the DLSR's are far less money! Saving money is a good thing - maybe can spend it on more aperture! :-)
..george
Well, an entry level DSLR camera is probably cheaper than a good CCD camera, but I have some concern and remarks:
1) I was told that the shutter of a DSLR camera doesn't last too long. After 20/30/50/100 thousand exposures it needs to be replaced. This takes money. (The more expensive the camera is the more the shutter lasts.)
2) The pixels of DSLR camera use rgb filters in a 12x12 Bayer matrix. That means that for photometry you either use g, b or r pixels so as a consecvence the effective resolution of the DSLR camera is worse than a similar CCD.
On the other hand you can get color photometry with a single shot (no need to filter wheel), but it need to be transformed to standard BVR system.
So if I had more money I'd use CCD with standard filters...
One more thing:
A DSLR camera is compact, easy to use when you travel. Even withour an EQ mount you can make some short exposures and do some "barefoot photometry" - at least for bright stars it can be an option, especially if you make stacked images. (With 14x2s exposures I can reach around 12.5-13.0 mag limit using 300mm focus at f/5.6 aperture.)
Well, ur comments make one thing clear - no I band. A lot of what I've been doing are long time sequeneces in I and B. If there is going to be a shift from CCD to DSLR do we risk a drop off in I band data? And to a lesser extent U, though U band is not common among amateurs. It seems to me if DSLR's bring new people into the field - great! If the ease of use reduces the number of data points outside g,b,r - not so great.
Yes, if you want UBVRI photometry, you need to use CCD with UBVRI filters. DSLR cameras are a good entry point for amateurs. You can easily make exposures, store the trails of photons and reduce them any time, even can transform the r,g,b instrumental magnitudes to BVR. But a standard UBVRI photometry requires CCD with UBVRI filters.
One other thing: many deep sky imagers use modified DSLR cameras. That means the biult-in IR filter is removed. In this case IMHO you can almos forget photometry because of the IR contamination - but I might be wrong...
My question is very basic, but I have not been able to find a reasonable answer so far. Is doing photometry with a single-shot color camera treated and processed like a DSLR? If so, what are any differences, and if not, how would you deal with using a single-shot color CCD camera?
Phil Evans
If you can make RAW images and process the r/g/b channels separately, then it can be treated like a DSLR camera IMHO.
[Note - I have no experience with single-shot color cameras of any type. But I built the Cookbook CCD kit and have used or tested about a dozen commercial monochrome CCD's.]
Every camera needs to be tested and characterized: (If a single-shot camera landed in my lap and I wanted to use it for photometry....)
- read noise
- gain
- dark current
- range over which it's linear (or ways to linearize the data if the detector is not linear over a large range of pixel values)
- bit depth and dynamic range. (I love my 16-bit CCD's...I can use comparison stars and targets that are up to four magnitudes different...and still get decent results. This level of performance may be very difficult for 14-bit systems, and impossible for 12 (and 8) bit systems.
Every filter needs to be tested and charaterized:
- how well does each filter match various standards?
- use transformation coefficients to put your data on a standard system of some sort.
As you learn and master your rig, you can better take advantage of its strengths, and avoid/minimize its weaknesses.
Point to ponder (since I have some scopes here with BVRI filter sets, and some with Sloan g'r'i'z' filters): If single-shot color cameras and DSLR's have some filters that are not close to B V R I...but are perhaps closer to Sloan g' r' i' z'....perhaps some of the transforms should be to Sloan? (My understanding is that the green channel is pretty close to V, but blue and red....maybe they are a better match for Sloan g' and i'?)
And then you must use the single-shot camera with a camera lens/refractor/other optical tube assembly:
- what star profile size is necessary for good photometry with a Bayer array camera? (do you have to intentionally defocus?)
- what field of view coverage do you want? (what focal length do you need?)
- how long can you expose, and how well can you calibrate for dark current/thermal noise?
You may find that some targets/projects are not easily done, but there shold be many other targets within your reach.
Don't stop asking questions.
I hope this helps.
(Wearing my Members
Folks:
(Wearing my Members Hat and my Staff Hat side by side. Boy that really has got to look weird! :-) )
As Aaron mentioned we're looking at migrating the DSLR things over from Citizen Sky and that will be done as he notes. For my part, pending management approval, I've volunteered to be one of the moderators of the DSLR forum when it comes online. I've started simple data-based astrophotography with my 15cm Newtonian last week, and have looked at getting a DSLR camera both for normal camera work and for scientific data gathering. I'm very, VERY much a newbie in this at almost every level, so I'm looking forward to growing with the Photometry and DSLR group as it evolves!
-----
Doc Kinne, KQR
AAVSO & ALPO Member
I'm glad to hear that DSLR Photometry is still on the playing field ! I was a member of AAVSO before Cit Sky - but that was more of a entry level program that got my interest. I struggled with the DSLR team and forums for 18 - 24 months: Gave up on IRIS a couple of times. With a great deal of help from Internet friends in Italy and San Paulo I've been able to work around the C S tutorial and actually have IRIS working. It's one more "spare time" project to venture to a new observing campaign - find comp stars & go beyond the Eps Aur Documentation & Reduction. - But its getting there ...
Best of Luck Doc and I'll keep checking in on the Forum. -- I realize these programs live and die by grants and funding -- I think this is a good program.
Sincerely,
Walt "Doc" Fahey FWJA
Dear Folks,
I started with "bare foot" DSLR photometry (8x5s stacked images with 75mm focus and 14x2s with 300mm focus) with my Canon EOS1000D + a 75-300 zoom objective in January 2011. Then I've got a tool from a friend, with it since May I was able to make 4x30s images at Polaris Observatory, Budapest. In September I purchased a Skywatcher EQ5 + drive, since that time I can make 30s images from our new home, in the southern part of Budapest too.
With the 300mm images my main problem is how to determine the Tbv and Tvr transformation coefficients, since the Landolt Standard stars are too faint for me. I've told this to Arne, so hopefully a set of BSM photometry will be available for DSLR users in order to help ctreating the transform. coeffs. One of the field for calibration will be the Coma Cluster, centered with more or less near GN Com. Until then I submit only "TG" photometry data.
Being a free/libre and open source software activist I use IRIS with WINE (windows emulator) on my Ubuntu 10.04.
Recently I make 10x30s images of some dwarf novae and LPVs on almost all clear nights. From Budapest despite the light pollution I can reach 14.0-14.5TG limit. With a collaboration of a friend of mine we regularly check most of my images for new transients as well. A few days ago I started to prepare a spreadsheet where I list the bright galaxies visible on the FOV of my target variable stars.
[quote=FRF]
With the 300mm images my main problem is how to determine the Tbv and Tvr transformation coefficients, since the Landolt Standard stars are too faint for me. I've told this to Arne, so hopefully a set of BSM photometry will be available for DSLR users in order to help ctreating the transform. coeffs. One of the field for calibration will be the Coma Cluster, centered with more or less near GN Com. Until then I submit only "TG" photometry data.
[/quote]
With BSM, we now have about 25 BVRI calibration nights for Coma Berenicis; 200 calibration nights for IC 4665, and 400 calibration nights for M67. These calibrations go from about 5th magnitude to 10th magnitude. I'll try to finish their processing in July and get them into VSD (June is booked solid, unfortunately).
Arne
Hi,
Those of us lucky enough to be south of the equator have access to the E-Region standard star fields (9 regions equally spaced around the sky at -45 degrees Declination). These have very good BVRc photometry of up to 100 or so bright standard stars in each region. There are always several E-Regions visible.
My Canon 450D + 180mm lens has a field of view about 7 x 4.7 degrees which encompasses about 20 standard stars between 6.5 and 8.5 V mag in most E-Regions. This is more than enough to determine transformation coefficients.
If anyone is interested, I have an Excel spreadsheet (based on data from Brian Skiff) that has the E-Region information. Cheers,
Mark
I knew we
Robert (et. al.):
I knew we were somewhat alike. I am one of the FOSS advocates here at HQ as well, although, truth to tell, its an easy job over here.
You're still running 10.04? I just got done migrating all of my personal stuff to 12.04 and have been pretty pleased with the migration.
I'm glad you mentioned the Cannon camera. A Cannon EOS is what I'd basically decided to get (I don't quite remember the model number now), but then I got busy with other things and need to get back to buying the camera.
I'll embarassingly admit that I don't know much about transformations (something that Arne has vowed to fix!). I've not used them in CCD observing, although I know I could. However, virtually everything I've come across dealing DSLR photometry has mentioned transformations. Are they that big of a deal with regard to DSLR photometry reduction as opposed to CCD reduction?
---
Doc Kinne, KQR
AAVSO & ALPO Member
Yes I still use 10.04 (LTS), since my hard disk is completely full, and I don't have enough room on any partiotion to try the 12.04. On the other hand I don't realy like Unity, so maybe when I "upgrade" it will be Linux Mint with some classic GNOME environment.
Regarding trasnformation it is essential since the color response of the RBG channels of the DSLR cameras are very much different from the Johnson/Coisuns BRV filters (eg. Tbv is around 2.0 for Canon cameras). So especially for LPVs the transformation is essential. Otherwise you just report 'TG' magnitudes, but they are not comparable to CCD V magnitudes.
Fortunately I've got a spreadsheet from a friend of mine to determine Tbv and Tvr + another one to make transformation from intrumental rgb magnitues to BVR. My preliminary results are quite good, but I'll wait for Arne's BSM photometry for final calibration of my camera's Tbv and Tvr. (On the other hand I think I need to recheck the transformation spreadsheet, since it seems to me there must be some error in the way how it transforms rgb to BVR.)
By the way I this it would be useful to prepare a software like VPHOT for DSLR user which can determine the Tbv and Tvr + makes the transformation of the instrumental rgb magnitudes to BVR...
I know one of the leaders of HAA/VSS is considering to write a script for IRIS to process and calculate the photometry data, but I'm afraid he is too busy, so I won't expect it within the forseeable future... :(
Hi All,
FRF (Robert?) commented on the need for software for processing DSLR photometry. I use both AIP4WIN (commercial) and C-Munipack (freeware) depending on the observing project. Both do an excellent job so I have not tried other software yet.
Both programs extract one colour, e.g. green, from the RAW image which is then calibrated and measured. The operator needs to start the process again to extract blue data and then a thrid time for red data. On my laptop computer (Acer Aspire 4740G, i5 processor) a times series of 500 images takes about an hour to process each colour channel. This is a very tedious.
It would be a major advantage if softare could be developed to extract all three colour channels in one process, apply appropriate dark and flat field corrections and measure star intensities. Is such a program currently available? Would Richard Berry and David Motl be interested in implimenting this in their wonderful rograms?. Cheers,
Mark
DSLR photometry is a growth area for variable-star astronomy. That does NOT mean that you should run out and replace your current CCD camera with a DSLR. The intent is that DSLRs will provide a means for beginners and those interested in bright stars to be able to make digital measures. A DSLR has a fixed set of filters (tricolor RGB) that don't match the Johnson/Cousins system (G is ok; the others require careful transformation); it does not have TEC cooling, so cannot expose very long; the pixels are very small and have limited well depth; the ADC is often 12-bit instead of 16-bit; etc. DSLRs are a great entry system (especially due to their lower cost), but a CCD camera has more applicability.
Arne
It is very exciting to me to find this topic of DSLR Photometry! I am trying this now, and I have learnt a lot from reading your comments!
As Mr.Fidrich and Mr.Henden have said, the DSLR is a relatively economic, portable, and convenient means of instituting photometry, so it is expected to be popular in beginners. Since I am a Chinese student who usually take trains to go out for observation, I may prefer DSLR to CCD.
And... Mr.Henden, Could I ask, if I should report the filter type as "TR","TG","TB" or "Rc","V","B", if I have done the transformation? Thank you!
Simiao
If you have done transformation, you can report "V", "B", "R" otherwise "TG", "TB", "TR". It is worth mentioning in the "remarks" field that that this was DSLR photometry. I paste below one of my records:
GU And,2455916.259,12.48,0.06,TG,NO,STD,ENSEMBLE,na,114,13.646,na,1,6065P,DSLR Canon EOS 1000D
Thanks for the info. There's a lot to test and consider.
I was looking at the Orion StarShoot G3 Color camera. They do have the camera available in monochrome and I know that would be a better option, but I am on a fixed income and unable to putchase both cameras. That's why I was considering the color one. (Thought I'd get more use out of it!) But, if necessary, I'll go for the monochrome and deal with the filters.
The telescopes I have immediatly available to use it with are a Meade 8" SCT at f6.3, a Celestron 8" SCT at f10, a 4" achromat refractor at f6, and a 4" Mak/Cass at f13.1. I also have a 12.5" f7.5 newt that is is undergoing a complete rebuild. (It has a mirror made by John Dobson in 1968, but it will be some time until it is ready for use again, as it will be set up on a new "horseshoe" mount in a permanent observatory).
Following are the specs (as provided by Orion) for the color version of the camera...
CD Camera Model Orion StarShoot G3 Color
Imaging sensor Sony ICX419AKL CCD (1/2 inch format)
Imaging sensor size 7.40mm x 5.95mm
Pixel array 752 x 582 (437,664 total)
Pixel size 8.6 x 8.3
Imaging chip Single Shot Color
Autoguider capability Yes
Exposure range 0.01 seconds to indefinite
A/D conversion 16 bit
Thermoelectric cooling Yes
IR filter No
Mounting 1.25" nozzle, 2" nozzle or t-thread
USB connection High-speed 2.0
Software compatibility Windows XP/Vista/7
Full well capacity 50000e-
Read noise (RMS) 9e-
Dark signal (at 0º C) 0.01e-/pixel/sec
Gain 0.79e- per ADU
Binning 1x1, 2x2
Max cooling -10C from ambient
Full frame download time 2 sec
Backfocus distance (from T-threads) 19.00mm
Weight (oz.) 12
Warranty One year
Images saved in... FITs format
If anyone has any comments about this camera or any knowledge about it suitability for photometry with any of my scopes, please let me know. Or, if you know of a better camera at a similar price, I would appreciate the info!
Regarding the Orion StarShoot G3 Color camera:
Pros:
- regulated cooling - not typical at this price range...can make calibration easier.
- pixels are not super-small, decent well depth for photometry
- filters built in...no need for separate filters and filter wheel...keeps cost/size/weight down.
Cons:
- cooling amount (10C) is not very large...I wonder if there is a simple 'hack' or modification to boost that to 20C?
- chip is not very large, so I recommend you start with a shorter focal length system, such as your 4-inch refractor. Later you can try longer focal lenghts, but FOV will be small. If you have planetarium software that can display CCD coverage on the sky....try out your various scope options with this CCD chip. FOV smaller than about 15 - 20 arc minutes is tough to point/find objects.
- pixel array does not have many rows/columns: 752 x 582 (you could think of it as possessing an 'image resolution' of about half that, or 375 x 290) ...and if you then put a Bayer array on top of that you cut resolution even further. Hmmmm, I would be willing to accept a single-shot color Bayer array on a chip with a million pixels, but not on this smaller chip.
Questions:
- is it linear over most of its range or not? I see no mention of anti-blooming, so I assume it's linear until you get close to full well.
- Can you live with a monochrome camera and one photometry filter (probably V) placed in the nosepiece? That would also keep size/weight/cost down, compared to a full filter set and filter wheel. (But no easy option for color images.)
- How much experience do you have with goto scopes, pointing models, and other 'hands off' observing methods? (I don't like adding flip mirrors into the optical path...they add the potential for flexure and consume back focus that may force you to modify the focuser so that you can reach focus. And if you automate more so that you can take data while you sleep, the flip mirror becomes usesless.)
These were just the first few thoughts that crossed my mind.
I am interested in trying DSLR photometry on bright stars, but I ran in to a problem regarding software: I am a Mac user, and could not get Iris running properly using Wine.
Is anyone doing DSLR photometry with free software that runs on Mac? Suppose it could be done with IRAF, which installs on Mac OS X, and there are perhaps other alternatives. (Or maybe some trick to be done to get Iris up and running on a Mac.)
Would be great if the upcoming DSLR manual could have a section geared to Mac users!
/Gustav
Hi Gustav,
What is your problem using IRIS via Wine? For me it's OK in Ubuntu, and maybe I can provide you some workaround that might be useful in OSX too.
If the problem is converting the raw files,
convertraw rawfilename img number
in command line can help.
An example:
convertraw khicyg121109p img 14
(If I made 14 images of the khi Cyg field on 9/10th November.)
Clear skies,
Robert Fidrich (FRF)
Hi Robert,
It works!
Yes, the problem was that I didn't understand how to convert the raw files without the drag-and-drop functionality that is missing in Wine on OS X. Your suggestion worked perfectly - thank you very much!
Clear skies,
/Gustav
Hi, My first post to this list; thanks Robert for the earlier response.
I’m also trying to get IRIS to work on a Mac using Wine Bottler. I get this response when I hit the return key- after I type in the convertraw command as you have it...
Impossible to read file
Users\Pc_check\desktop\asto\sample_data-images\img_3147.cr21.crw
Any ideas about where I’m going astray?
Thanks!
CSS
Hi forum,
I have followed the Dslr photometry program for eps Aurigae described in CitizenSky and i have started to move the first steps. However I have a doubt about completing my analysis using the beginner spreadsheet.
In "Comparison Star Table" section i put the values of instrumental magnitudes obtained with IRIS program for all the comparison stars and check star.
But I really don't understand what to put in the section "Target and Check Star Calibrated Magnitudes" in order to obtain the average values. How can I obtain the several values of magnitude both of the check star and the target star? Do they come from several sets of photos and measurements? And in this case, what values I have to put in "Comparison Star Table" section? and finally, if the average magnitude values come from several sets of photos taken in different moments of the night, how can I assess the right Julian Date?
Sorry for the newcomer question but I would really appreciate if you would solve me these doubts.
Good morning everyone, I start a thread in the forum in Spanish about photometry with werbcam , as I speak very little Spanish I visited the forums in English of the AAVSO, but today I decided to take some time to do, and find this topic transformations band rgb to BVRc seems to be very modest photometry with a device like a webcam , although many observers (not the AAVSO ) have done , not conosco of anyone who has done photometry with transformciones using a webcam. In my case I use an IR cut filter ( Baader IR Cut ) relations b-v color to B-V and v-r to R-c are nonlinear and change with the air mass. I have also made measurements with webcam and a filter Opteka R72 , which is a filter that blocks the optical and passes only IR, in this case the b y r channels are inverted in their function (r captures the region near to the optic, and b the farthest in the infrared region) this can be transformed to magnitudes i ' and z'sloan , which I' ve already done, i have reached the precision in measurements by stacking 30 images was 0.03 , (which to be a webcam I feel very good since we know its bit depth is only 8 bits , 256 levels of brightness in individual shots linearity is lost at 214 ADU where starts funcioner anti -blooming ) , I am developing a software called RGB Fotocalc performing transformations automatic way after saving the coefficients for three different air masses , since the interpolated intermediate values to correct any air mass , the explanation of everything I have done is a bit long to write here , for the time I leave page where I have posted this personal project :
http://olichris.jimdo.com/rgb-fotocalc-software/
this program I am still writing and still have not finished it , but they manifest this because the methodology I use is identical to the user of DSLR cameras , and with whom I share this information more . I'm writing a document with information about this I hope to have ready in January or February, but I still need a little .
I do the photometric measurements in the Astroart software , which allows separate RGB components in the window itself necesidada operations without having three separate files , that DSLR is very good. the instrumental values write in my software and transforms , although using spreadsheets can use yours .
The webcam is a camera that use Celestron NexImage (CCD SONY ICX 098AK ) is modified for long exposure and has two additional amendments , one for turning off the power of the silicon substrate , so that I can take exposures up to 15 minutes with the quality a much more expensive CCD , and another to remove the internal preprocessing save the captures in format RAW. In this short paper I show the results of these changes .
http://olichris.jimdo.com/astrofotografia-de-investigacion-webcam/
or more directly
http://olichris.jimdo.com/app/download/1967035218/52b74a09%2Fd4ceec214c…
I will continue informing them about my work . In the near future I intend to work in the YSO reporting section that is what has always loved and now AAVSO available, it falls to me like a glove .