DSLR Documentation and Reduction

Hi Brian,

Congratulation, i saw the article onSky & telescope. That is great. But i still have some questions:

1- for some stars likeAlgolon Pers, 10-30 images that made one stack, is enough per night? i mean that one stack can record all the data that related to star's light?

2-On cloudy nights, small clouds can effect on result?

see u

ichi

Hi Ichi, These are good questions. Could I ask a favor of you? Could you re-post these questions to the Photometry Forum on the Citizen Sky Website so that others may benefit from our conversation? I'll re-post my reply below there once I see your post. To answer your questions: 1) Yes, a stack of 10+ exposures taken over ~10 minutes is often good enough to reduce the intrinsic error in the detector such that accurate photometry can be achieved. As far as I know, nobody has done studies to see what limiting magnitude can be achieved using this technique (especially because you'll need a moving mount after about 6th (?) mag). 2) Yes again. Clouds can adversely affect your results, namely because they decrease the total number of photons reaching your detector. Given that cloud cover is seldom uniform, the target and calibration stars will be dimmed by different amounts, thereby ruining the calibration. So you should avoid observing when it's cloudy/foggy if possible. Have a good day, Brian

Hi Ichi, To answer your questions: 1) If you collect data over time you can plot (using Excel or something else like VStar) the magnitude vs. date. This will help you build up your light curve. 2) If the period is obvious, you can phase it yourself. Otherwise a program like VStar or Period04 should help out significantly. 3) Algol is very well characterized (with a period known to six decimal places) so additional data on this star may not be too useful from a scientific perspective. It would, however, be a good target for you to see how well your data collection and analyais procedure works so I'd say give it a go! Have a good day, Brian

Hi Brian, ok, thanks. Briando you think if i use only instrumental magnetude in polts, can i have acceptiable results? Or i should calibrate them? ichi

Hi ichi, You could use just the instrumental magnitudes if you wanted only differential measurements (i.e. relative to some earlier time), but it's much more useful to put the measurements into a standard photometric filter, like V-band, that way your measurements can be compared with others. The Finishing Analysis tutorials should get you to the calibrated point (it's actually much easier than extracting the Imags and even includes air mass corrections!). Cheers, Brian

Hi Brian, is the dimension ofimageeffect on result?I mean dimension of the images that are taken by Canon20D is2336?×?3504 but for Canon kiss x3 dimension is4752?×?3168, i thinkit is relate to CMOSpixels and their arrays, So can this effect on result? see U ichi

Hi Brian, Hi everyone, Iencounter a strange problem with AIP4WIN, i use it for citizensky simple_data package and it works, but it can't open my images which are taken in CR2 format. I can open them in IRIS 5.59 and Maxlm DL 5 and some image editing programs in Mac Os like Perview an Aperture,but i can't open them in AIP4WIN 2.3.1, and it says it can't decode the digital camer image. Even i had tounistall the programe and install it again but no thinghas been changed.All ofmy images are taken by CanonEOS kiss x3, in Canon raw image format (CR2) and size ofmost of themare 16-17 MB. What is your suggestion? ichi

Hi Ichi,

hi everyone, Tom thank you for your comment, i sent a massage to that group so i will wait for reply. But i have some questions related to Iris and Maxim dl: In Aip4win we calibrate and stack the images and then measure the magnitude of varible star on stacked image, but in Iris and Maxim dl tutorials:

1. (Iris tutorial)
2. 3.Repeat the photometry steps for each image you have taken recording the instrumental magnitudes as you go.
3. teps for each image you have taken recording the instrumental magnitudes as you go.
5. (Maxim dl tutorial)
6. step13
7. Record this value from each star and then select your next image and record the instrumental Magnitude for the same stars.
9. i should calibrate and stack the images and then measure the magnitude on each of the images? do i get it correctly? if yes, so why do stack the images? if no, what does each image you have taken mean ? Are they refer to next stacked images? see U ichi

Hi Ichi, Just for IRIS: It's true thereis that strange sentence at the end,you areright if you stack all your images you make only one photometry operation of the singleresulting image. But doing this is not the best, in fact it's better to separate the images in three or five groups for stacking and then you make the photometry of such three or five resulting images fromthemultiple stacks. This allows for making a sigma (standard deviation) calculation that is a good indicator of the uncertainty level of the session. That uncertainty isdue either to the SNR optimisation that results from your choice of shooting condition or the sky condition. This is away to improve your shooting condition (maximizing the electrons accumulated from each star in each shot: defocus, exposure time, focal lenght/aperture size, ISO as low as possible for such bright stars... ) or reject session due to poor sky condition (it could happen evenunder clear sky) There are also people who do not stack at all and make the photometry of each picture and then are able of calculating a true sigma and possibly applysigma clipping... ( I agree a sigma on 3 or 5 values onlyis not very accurate ! ) In fact there are two versions of that IRIStutorial on the site, one under "IRIS-beginner" another one under the wiki pages. The"IRISbeginner" version is an old one thatincludes number of errorsand has not been updated,I don' know why it's there. The most recent (but not perfect ! ) isat the wiki pages (maybe needs to activate mebership). Anyhow it also needs a serious revision... Yours truly, Roger

hi Tom, I want to attache one of the images, but this error appear: Validation error, please try again. The file you attempted to upload may be too large. If this error persists, please contact the site administrator. Can i upload CR2 files? ichi

Hi Ichi, CR2 files are not an allowed upload format. Just smaller files like JPEGs, PNGs, PDFs, etc. You'll have to send the files directly. Brian

Hi Ichi, Sorry the upload didn't work. I wasn't aware of the restrictions that Brian mentioned. Did you try opening your files with version 2.4.0? Richard may have included the capability in his latest update. If you want to try emailing the file to me directly we could try that again, too. Tom

Hi Tom,

Hi Brian,

Thank you for your responsibilites.

At last i opened them in 2.4.0V. thank you again ichi

Hi Ichi, Glad to hear that version 2.4.0 did the trick. Tom