Teams / DSLR Documentation and Reduction

DSLR Documentation and Reduction

Citizen Sky is now officially permanent part of the AAVSO. In the coming weeks we will be moving additional content to the AAVSO site and freezing this site as an archive of the 1st three years of the project. Please visit the new landing page for future updates.
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Citizen Sky
We will discuss how to get the best results from a off-the-shelf DSLR camera or point-and-shoot camera by creating guidelines on how one can characterize a camera and create low- and high-level tutorials for various software packages. These documents will be contributed to the Citizen Sky Website.

Camera "Recommendations..."

Hi Folks:

Yes, I'm coming very late to the party, but I think that DSLR photometry will have a long life after our little project here.

The documentation that I've been able to read, both here and elsewhere, has concentrated, perhaps rightly, on image post processing. I'd like to talk about the camera for a second.

I'm currently looking at two cameras:

The Cannon EOS Rebel T3
and
The Cannon EOS Rebel T2i

Now I realize that the camera has to output in RAW format, and a manual shutter control and I'm trying to track down the manuals to these cameras to get full details on them. That'll be the best research source.

However, I wanted to see if anyone here has anyone here has any experience with these cameras.

Thanks, folks!
----
Doc Kinne

Beginner reduction spreadsheet valid at all air masses?

Submitted by Roy on 23 November 2011

I've had an email exchange with Brian off the forum on this topic. I thought it might be of interest for others to see what I've been doing.

In the documentation on DSLR photometry, it is stated that the beginner reduction spreadsheet should be used only at relatively low air mass.

I've done some tests on a star field in Grus, with only slightly more than 1 degree separation between the comp, check and target stars (DSLR images taken through a 600mm focal length refractor).

The results suggest that the spreadsheet can be used at any air mass with no or minimum loss of precision. Remember, this spreadsheet does not specifically include calculations to correct for air mass.

I'd be curious to hear if anyone else has tried this. If you haven't, you might find it interesting to give it a go.

Roy

Help with tutorial

Submitted by ptsouth97 on 25 September 2011

Hello,

I finished the IRIS beginner tutorial, but my results seem to be off.  I feel pretty confident about steps 1-5, but I may have made a mistake in step 6, photometry.  In Step 6 a, the tutorial mentions configuring the magnitude constant, but I do not see where this is explained.  As a result, I left the magnitude constant at 0.0.  Maybe this is throwing off my results?

Here's what I got for Instrumental Magnitudes for the Comparison Stars:
Iam Aur -10.747
rho Aur -10.339
mu Aur -10.671
ome Aur -10.616
sig Aur -10.364
58 Per -11.190

I only took these values from one of the final separated green channel files.  Is that right?

m = 0.111
b= -15.555

Average Check V Mag = 4.743, which is more than +/-0.01 from the 4.705 V Cat

Finally, my average V Mag for the target star was 3.741Read more

Reporting reductions of historic plates

Submitted by Bikeman on 13 September 2011

Hi I have been experimenting with reducing scanned historic photographic plates lately, and I guess at some point I will want to report the reduced data to the AAVSO DB. But how should that be done? I think it would be more than wierd if my observer code would be next to a measurement that was done in (say) 1904.... Some credit must be given to the original observer, and the observatory and plate Id somehow should be encoded in the limited size of the comment field. But how exactly? Any suggestions? CS HB P.S.: I seem to have to limit the audience of this article to one of my groups In order to post it??? Is this a new website feature or a bug?? :-)

Canon 5D MkII photometry

Submitted by ewiley on 31 August 2011

Embarrassing as it is, I am just now gearing up for some photometry. Has anyone determined the transforms on a Canon 5D Mark II? I am assuming it will be different than my 450D. I will be working with a Canon 100mm Macro and have a Kenko Sky Memo which allows tracking of 5 minutes without guiding. So--I am thinking I need to characterize this camera using Landolt fields. If skies during the Okie-Tex star party cooperate I should be able to get several nights worth of data. Any suggestions would be appreciated.

Ed

DSLR photometry of close binary, Delta Cep

Submitted by mdurkin on 28 August 2011

Hi everyone,

Earlier this month I took some wide field images of the area around Cassiopeia and Cepheus for photometry measurements.  I was able to make a measurement of Delta Cep, however my measurement includes both components of Delta Cep, the variable plus it's fainter companion at magnitude 6.3.  My question is, since I can't split the components of Delta Cep in a DSLR camera, should I submit the combined magnitude or should I calculate the magnitude of the variable primary by mathematically removing the fainter companion (a difference of 0.12)?

Thanks,

-Mike Durkin

New Spredsheet version with optional extinction correction

Hi all

Since the old thread was somewhat framgemented I thought I'd start a new one.
For most observers eps aur will now be observable at relatively low air mass, so I thought it might be a good idea to extend the Excel sheet with a simple "toggle switch" that will switch on/off air mass correction. In the attached file, you can do just that in cell F51

1 ==> air mass correction is performed
0 ==> air mass correction is not performed (= extinction coefficient is set to 0. No need to input observation location coordinates and observation time in this case)

Note that for both cases, the error in the comparison star mag fit is shown, so that you can actually see by trying both settings which method gives the better fit. Read more

New spreadsheet with automatic calculation of Tc and k'

I haven't noticed the Teams before and have now joined the DSLR team. I have uploaded my spreadsheet for reduction under "Final Reduction". This is the sheet I have used all along the campaign and it has worked very well. It has an automatic calculation of Tc, k' and Zp using the least-square method between the compairsion stars. After the coefficients is calculated they are applied to the variable star (epsilon in this case). Read more

zero point, AIP4WIN

I am currently trying to get to grips with the tutorials for both AIP4WIN and IRIS in terms of analyzing DSLR images.

In the AIP4WIN package, relating to the eps Aur sample images, what is a suitable zero point?

All the best,

Chris Allen / Sweden
www.variablestarsweden.seRead more

eps brightening during June?

Credible DSLR reports have been received that epsilon Aur has been slowly but steadily brightening during June, perhaps by as much as 0.10 mag +/- 0.02 mag, toward 3.70 lately. Corroboration requested.

Figured out Air Mass Corrections

Greetings!

Just last week I completed my last finals, ever. Just Ph.D. work from here on out! I had a little time to work on air mass corrections. I've figured out a way to do it, now I just need to finish out the math for a least squares fit to points to make a plane. More details to follow later.

BrianRead more

DSLR Imaging Tutorial

Imaging with a DSLR and Simple Tripod

Most of the imaging procedures for DSLR photometry will be very familiar to those who have dabbled in astroimaging. The goal of photometry, however, is to accurately record, not appearance, but the relative brightness of each star compared to other stars in the field. This accuracy is achieved first, by calibrating each image to eliminate both electronic and optical anomalies of the camera and second, by stacking multiple exposures. Stacking increases the signal (star photons) to noise (background photons) ratio and averages out the effects of atmospheric variability. Also, be sure to record all your images in "RAW" format.Read more

Number of stars used in Final Reduction

Hello (again!)

As I was playing around to find a simpler procedure for IRIS I noticed that the output values depend (a little) on the number of stars used to calculate the TC.

I was using the reduction-beginner spreadsheet which calculates the final values for the check star eta Aur and eps Aur. When i was using only the eta aur and zet aur I was getting the normal value 3.172 as output value for the check star and consequently a value for eps aur.

When I was using more stars (in our sample data for example I took into account all available stars) I could get some values close to 3.172 (like 3.174, 3.179) but some further away (like 2.966). The output values for eps aur in this case were not so much different than when I used only eta & zet aur. So it seems to me that there is not really a need to put so many stars there.

Am I missing something?

Regards

GrigorisRead more

IRIS: a simpler procedure !

Hello to all!!

I have made a presentation of the procedure in IRIS to some friends but the argue that this procedure seems to confusing. One of them, that he is already active to the project and sending data to jeff Hopkins, told me that because of the small exposure time there is no great need for bias,dark,flat frames. So i went on to remove these steps and after many tests with our sample data and others I managed to simplify a little bit the procedure. So perhaps, this (http://www.citizensky.org/teams/dslr-documentation-and-reduction/iris-tu...) can be a beginner's tutorial and the one that we have now to become an intermediate tutoria (since we take into account more accurate steps).

Perhaps, someone else can check this to see if it is correct. One point that still have not clarify is the adding of images. I see that both arithmetic and median works, but i suppose that median should lower the S/N. So is it better then to select only the arithmetic method?

Regards,Read more

Airmass / Extinction

Hi all!

As summer is getting closer, I think it's time to look at extinction/airmass.

While some reduction packages have an airmass claculator, others don't, so I think it would be best to integrate airmass into the Excel spreadsheet.Read more

Tutorial DSLR Finder Chart

A finder chart with all the check and comparison stars from the Beginners Tutorial Reduction spread sheet.

For the curious: derived from a photo taken in mid February 2010 with an Olympus E 420, f= 55 mm, f/4, 9  x 8 sec, ISO 400, defocused.

It shows stars in the field down to approx 8 mag.

Attached is the ready-to-use PDF version.

I checked the star labels by putting a printed page over a flat screen showing a Stellarium view of the field, so I'm pretty confident they are right :-)

I also attached  an editable  version (OpenDocument Graphics format, created with StarOffice).Read more

Finder Chart ideas

I thought it might be helpful for beginners to have a finder chart that shows all the stars mentioned in Brians spread sheet and which looked a bit more like an actual DSLR image of the field.

This is harder than Ihad expected. If you add too many annotations, it somehow destroys trhe overall impression of the field .

I'm also not convinced whether a normal or negative image should be used. Negative is definitely more user friedly for printing.

Anyway, attached are a few of my ideas, please let me know whether any of those might be useful (my favorite is the multi-page one).

CS
Heinz-BerndRead more

IRIS tutorial review

Hi team!

I made a test run of the Iris tutorial with the sample images that Tom donated. I had a few problems so I changed the tutorial a bit, especially at the point when you extract the green channel.

I also made some screenshots that I sent to Brian in a ZIP (you can't attach ZIP files here and I was too lazy to attach each screenshot individually).

CS
Heinz-BerndRead more

Sample Data Posted

Greetings,

The sample data for our tutorials has been posted online. Tom has kindly provided the files for our use.

http://www.citizensky.org/sites/default/files/DSLRPhotometry/data/sample...

Size is 74.8 MB, files are in .cr2 format.

BrianRead more

Simplified Reduction Method

All,

I think I have a simplified version of the Excel reduction sheet ready to go. I think the math behind it is sound (see attached PDF), but I would like someone else to check it to make sure I didn't neglect anything.

For this introductory-level reduction method, air mass correction is absent, but then again the difference over the field-of-view of a DSLR camera should be small. This would simply correct the instrumental magnitudes going into the equations anyway so I think it's fine.

Let me know what you think,
BrianRead more

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