Forum Replies Created
-
Posts
-
I didn’t put them on the web, I wrote an feature in VSS circular about it and some other apps I had written. If you want a copy I can email it to you.
James
Applications are available for this, I wrote one myself a few years ago. I would be careful using the GCVS data as I found it was not very accurate. I used the Krakow University’s list as it is more up to date.
James
You could try running it in comparability mode in Windows 10, or use a virtual machine (like VMWare player) to host Windows XP).
James
I did consider the SkyWatcher version but felt that the weight might be too much for the mount. It’s a shame SW stopped selling the CF version as it was lighter.
If anyone can recommend another telescope for photometry with an ASI1600MM-C camera (3.8um pixels) ideally with all the required accessories (excluding mount) totaling less than £1000, though I might be able to go up a little more. I would prefer something with a focal length of 800mm or less to give me a wide field for selecting comparison stars. It will also need to get to fainter stars than my current 70mm f6 scope without needing longer exposures. Also it needs to be light enough for an AVX mount.
I’m considering the C6 + Hyperstar, Bresser AR102XS/460, StarTravel 120 (with upgraded focuser) & 150mm f5 Newtonian.
James
I think those area calculations are a bit out, looks like you did pi * D * D instead of pi * r * r.
However, if the seeing is making stars effectively extended objects surly the gain in magnitude will be related to the change in focal ratio not aperture, and the aperture increase will improve the signal to noise ratio as more photons are collected in total.
James
My current camera on a C6 Hyperstar will give 2.7″/pixel though I might also get a new camera and so this may change to 1.7″/pixel which would be better. My current system (ED70) gives 1.9″/pixel, so is a little under sampled.
This is all only a thought at the moment I need to see what the finances will allow.
I typically get 2.5″ – 3″ FWHM on my images using a 3.8um pixel size camera (ASI1600MM-C). I only use the middle quarter (area) of the camera due to field curvature.
James
As seeing will effectively make stars extended objects a low focal ratio should get me fainter stars without very long exposures. Combined with the larger apature to give me more photons and better signal to noise ratio, I thought a hyperstar would be a good choice. However I say a review that said they weren’t suitable for photometry, but it gave no explanation as to why, and I couldn’t think of one. To me it looked like a win, win situaction. How bad would undersampling need to be before it is an issue?
James
I have had AIP4Win running on Windows 10, but found that the software was so full of bugs and the writer was not interested in fixing them that I gave up on it.
I now use C-Munipack (http://c-munipack.sourceforge.net/) for photometry, as it will output BAA VSS format files and the best part is it’s free and well supported.James
I don’t know about pointing for Spectroscopy specifically, but in general even with a small field of view on the guide camera you could try plate solving. For locating variable stars I use APT’s Goto++ feature which takes an image, plate solves, syncs the mount to the current location and issues repeat goto commands until it is within a specified tolerance of the required location. I don’t see why it would not work with a spectrograph guide camera instead of the main imaging camera. Just connect APT to the guide camera use the Goto++ function the shutdown APT are start guiding as required.
I have never made one myself, but I had a looking through a similar setup made by Normal Fisher (I think that was his name) about 30 years ago at an astro camp in Ashdown Forest. It had un-silvered mirrors and no wedge, the view was a bit on the bright side compared with modern full aperture “solar film” type filters. It was about the same size as you’re proposing as well just over 8″ I think.
James
As I recall it gave very nice views.Grant,
It is used quite a bit for photometry, the variable star section has a spreadsheet that can read an analyse the output from it and convert it into a format suitable for submission to the BAA VSS database.
I would go for a EW type as they are continually changing in brightness and generally have short periods. Possibly VW Cep (mag. 7.2) if you are using a camera lens, this has a period of just 6h 40m so a full orbit can be captured in one night, it is also circumpolar from the UK so can be imaged any time of the year. Or possibly NR Cam (mag 10.76) if you are using a telescope for similar reasons, circumpolar, period 6h 8m.
What camera, lens/telescope are you using?
Before you take a time series in anger you will need to determine the exposure/iso you need for different magnitude stars, making sure you allow some spare space at the top end to take account of non-linearity in the camera, different star colours and atmospheric transparency.
James
A few other things I missed, I keep the ISO to a maximum of 800, so that noise does not become an issue and restrict the exposure to between 10sec and 30sec. Less than 10sec and scintillation in the atmosphere will reduce the accuracy of the measurements and longer than 30sec field rotation & tracking become an issue on an alt/az mount without guiding (its not possible to guide in alt/az mode anyway). I also avoid a 15degree radius of the zenith also due to field rotation due to the alt/az mount.
James
I don’t see why you couldn’t use the calibration in Nebulosity and then do photometry in Iris, though I’ve never used Iris myself. Below are details of the hardware, software and workflow that I use.
Hardware:
Canon 500D (modified) with red dot finder mounted on the hot shoe
Bahtinov mask
Canon 200mm f2.8 lens
Celestron SE4 alt/az mount
Bracket made from a binocular L mount and dovetail bar (to connect lens collar to mount)Software:
APT
Fitswork
Nebulosity 4 (demo)
AIP4WinCapture workflow:
Perform two star alignment of mount using APT’s liveview feature with crosshairs on.
Manually focus lens using mask using 1 – 2 sec exposures,I find APT’s bahtinov aid doesn’t work very well, so just look at the images on screen.
Capture 20 flats (same ISO as required for variable)
Capture 20 darks (same ISO and exposure as required for variable)
Use APT’s Goto++ feature to get within 100 pixels of the target star
Use APT to capture imagesNotes:
I have previously ascertained the correct ISO/exposure for a variety of star magnitude ranges so as not to saturate the variable or comparison stars.
APT’s Goto++ is a great way to centre an object and saves a log of time.Processing workflow:
Use Fitswork in batch mode to extract 3 colour planes into individual fits files for flats, darks and lights.
Delete the red and blue files as they of no use.
Use Nebulosity demo to preview the files and rename/delete those that have excess trailing or cloud, so these files are not used for photometry.
In AIP4Win setup basic calibration (darks and flats).
Use AIP4Win MIPT to analysis images (calibrating at the same time).
Import the AIP4Win data file into the BAA VSS spreadsheet to produce BAA database submission format files.
As well as submitting the photoemtry to the BAA VSS I also measure the timeings of minimums (using software I have written) and submit the times to the Krakow University database.Notes:
I have previously determined the read noise and gain of the ISO settings I use as these are needed by AIP4Win
I have a small utility to calculate the heliocentric offset, again used in AIP4Win.
Personally I don’t think much of AIP4Win and only use it so that I can use the VSS spreadsheet. It contains a lot of bugs and the author is not interested in fixing them.
For comparison stars I use the AAVSO VSP to produce charts and tables of suitable stars.The above works for me, I’m sure a lot of other software and workflows will also work. Good luck if you decide to give it a try and feel free to ask if you wat any help / advise.
James
If you want more details on how I produced the FN Cam measurements (as well as many others) I can provide you will more details.
James
Very sad news, I have copies of all books from 1965 (the year I was born) to 2016 (plus many duplicates). The end of an era.
James
Thany you for confirming that. I didn’t think there would be a problem, however I had come across a reference on the internet that said it wouldn’t work which set seeds of doubt and so didn’t want to spend the money on a mount only to find it was of no use. Might even try the DSLR with my old ST80.
James
I’ve now compared 3 different resources for the calculation and they all come out different! I’ve tried the BAA applet, a sppreadsheet I found on the web (HeliocentricJulianDay.xls) and the ohio-state.edu web site. For a test I’ve used an observation of NR Cam at JD 2457388.40539.
BAA app -> 4.609 min (276.54 sec)
Spreadsheet -> 281.3 sec
ohio-state.edu -> 344.98 secThe first two are less than 5sec different however the ohio site is over a minute off from the others. It would appear that they all use different methods of calculation that are not consistent! I’m wondering if there are issues with floating point rounding due to the number of significant figures required.
James
