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About woodblock

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    Star Forming

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    Painting, Printmaking, Astronomy, Growing Vegetables and Fruit
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    Shropshire UK

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  1. Thanks, I'd be interested to see your report. How would you send it?
  2. For the purpose of photometry suppose I want to limit my exposure time to say 20 seconds in order to minimize trailing but I want an overall exposure time of say 60 seconds. If I take 3 x 20 second subs does it make any difference if I stack them by addition or stack taking the median. Are they equivalent? They'd obviously have to be aligned before stacking. Cheers Steve
  3. What kind of thing might make it different in one direction as opposed to another? Why should it be different? If you had two observers one north and one south and if they each had a mirror and if each of them sent out a photon towards the mirror at the opposite end. Then suppose they could actually measure the speed of his own photon in both directions separately. If the speed did come out different in the two directions would they agree on which direction was fastest. eg north to south is faster than south to north for both observers. Or would they find that the outward journey
  4. I was following the AAVSO instructions for photometry using maximdl. In those instructions there is a point where it asks you to "Extract bayer plane". At this point you have to select 1 of 4 channels R G1 G2 B. You cannot select more than one channel. I've attached a screen shot. I think I'm only extracting one of the two green channels. The resulting image is half the width and height of the original image. In the other tutorials of the AAVSO guide it does exactly what you describe (for example AIP4WIN) but I think the one for maximdl really only looks at a single green channel.
  5. Thanks Vlaiv, What I was thinking was this. In the case where a scaling factor is used it is using the data from all of the green pixels. The green values for the red and blue pixels are interpolated. So half the pixels have true measured values and the other half has estimated values by interpolation. In the case where you extract the single green channel you have true measured values for those pixels and nothing at all for the others. You have one quarter as many pixels. Suppose you are doing photometry on a star. Lets say the image of the star is square and is 10x10 pixels i
  6. I'm trying to decide which software to use for photometry with my DSLR. AAVSO publishes a document which has tutorials for various software for the purpose. I'm currently looking at maximdl. In the AAVSO instructions the green 1 channel is extracted from the raw file and then the photometry is carried out on that. It seemed to me that I'm losing data since there are two green channels. I had a look at the instructions for a couple of other pieces of software and it's done differently. In AIP4win for example you extract the colour by putting in a scaling factor for each colour red, green,
  7. I'm using maximdl which allows me to extract a single channel from the raw file. If I understand correctly there are 4 channels - green1, green2, red, blue. If I extract one channel the resulting image is half the size of the original. So my raw picture is 4290x2856 and the extracted image (one channel) is 2145x1428. It's the same whichever channel I extract. But why is it half the size and not quarter size since I'm extracting 1 out of 4 channels? I'm doing this as part of my photometry work where the AAVSO say only use the green channel. Cheers Steve
  8. I found the problem - a box I hadn't ticked. It only took me about 4 hours to find it. Duh!
  9. I'm evaluating a demo copy of maximdl. I'm following instructions from a document on the AAVSO website but I'm also checking against the user manual. I've done the calibration, aligned and stacked the images and it all goes ok. When I try to do the photometry I can tag the object, reference and check stars but when I click on the graph tab the tab is completely blank. No graph or axes or anything. Does anyone know if that is disabled in the demo version? Everything else works ok. It correctly identifies the stars on all the other images. Cheers Steve
  10. That was the purpose of the exercise really - to find out what my parameters are with my setup.
  11. Last night I did some experiments on exposure times. I wanted to get an idea of the maximum exposure time without saturating the pixels. My scope is a 200mm SW newtonian and I'm using a canon eos 450d. I found with a star of magnitude 8.060 that the star image became saturated at about 8 to 10 seconds at iso200. I think they recommend an exposure time of at least 15 seconds so on that basis there would be no point with my setup testing a star with a magnitude less than say 9. It hadn't occurred to me before that there might be such a limit. The picture was sharply focussed so I can probably
  12. Thanks, Yes I will definitely check the backlash. I did adjust it a while ago but I didn't want to overtighten it so maybe I left it too slack.
  13. I have trouble getting the scope to point exactly where I want automatically. I use APT, cartes due ciel and eqmod. The mount is an heq5. I use cdc to drive the scope to the object I want. It gets pretty close but sometimes the object is not in the field. Then I take a picture and do a plate solve through APT and it usually gets a result in a few seconds. Then I click on synch (in apt) to set the scope coordinates to the plate solve result. Then I go to cdc, click on the object I want again and then click on slew in cdc. The scope moves. This is always a very small movement. But when I
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