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Everything posted by Altais

  1. I don't think CCD manufacturers typically state the gain of their sensors. But you might find numbers from others who have measured it. Or you can measure it yourself using the Astrophotography Lab program.
  2. Here is a version with a wider field of view.
  3. Oslet, I would actually suggest trying a higher ISO (e.g. 1600) if you aim to use short exposures. The ISO value is basically a tradeoff between read noise and dynamic range. With higher ISO comes lower read noise, which is always nice, but this comes at the cost of lower dynamic range. Actually, ISO is just a way of describing the concept of gain, which is the number of electrons (think photons) that must be accumulated in a pixel in order for its digital value to increase by one. High ISO gives low gain, meaning that the pixel value will increase more per electron and hence you get a "h
  4. Well, even though short exposures through narrowband filters will probably be read noise dominated, that is just a result of reduced photon noise from the (broadbanded) background. The total noise level will actually be lower, since you have the same read noise but lower photon noise. So for targets with significant narrowband emission, you should get better SNR using narrowband filters than RGB filters. But the fact that the subframes are dominated by read noise means that you in principle could improve SNR further for a given total integration time by increasing the duration of individual ex
  5. Yes, you can obtain an estimate of the brightness in mag/arcsec^2 from a light frame. But there are a lot of uncertainties in this calculation, so you should take it as a rough guideline rather than a precise measurement. The use of filters doesn't really affect the reasoning around signal to noise. But you should keep in mind that the narrower the filter, the longer you need to expose in order for the photon noise to dominate the read noise, since photons are hitting your sensor at a lower rate. This is why narrowband imaging tends to require much longer exposures than RGB imaging.
  6. Craig Stark has a really nice series of articles which I would strongly recommend for anyone interested in understanding signal and noise and how they depend on equipment and conditions. The articles can be found here: https://www.cloudynights.com/articles/cat/column/fishing-for-photons/ One thing he covers is how you can measure the gain of your sensor. I was inspired by this to write a program to do it automatically, which evolved to do a lot of other things as well. If you're interested the software can be found here: http://lars-frogner.github.io/Astrophotography-Lab/ It can be u
  7. I think there is a lot of sense in what you're doing. If our cameras had no read noise, there would in principle be no difference between the SNR of a single 10 minute exposure and stack of 20 half minute exposures. Then it would basically always be better to do many shorter exposures, since you would never over-expose parts of your target, you wouldn't need to do guiding, you can get rid of artefacts like cosmic ray hits and plane trails by stacking and the cost of a failed exposure is very low. (Of course, if taken too far the sheer number of subframes to pre-process would become prohib
  8. Thanks! I should probably have cropped the old one to match the new one so they could be compared directly. The old one is quite close to the full FOV of the camera, but with the new one I prefer a closer crop to better reveal the details. Here is a better comparison of new (first) vs old:
  9. Thank you very much! It's 274 frames of 6 minutes at ISO800 and 21 frames of 3 minutes at ISO1600 (so actually just 28.45 hours but 30 sounds cooler). The latter is the dataset from 2015 which I reused in the new image in addition to the new data. The reason I changed from ISO1600 to 800 is because I think the additional dynamic range you get with 800 is well worth the slight increase in read noise for this target. Yeah, it's quite amazing what digital sensors have done for amateur astrophotography. But then it's really humbling to look back at what people were able to achieve withou
  10. Thanks Ole Alexander, much appreciated. I live a bit north of Lillestrøm (Lindeberg i Sørum). It's sufficiently remote that light pollution from the cities is not a big issue (and also we have no street lights), so I get reasonably dark skies.
  11. Great work! Nice and round stars, a lot better than anything I've managed to do unguided. Let's just hope the great weather doesn't go away anytime soon.
  12. M51 is nicely positioned in the sky these days, so I've spent quite a lot of time imaging it lately. My previous (and first) attempt at M51 was four years ago. At the time I was struggling a lot with getting decent guiding, and had to discard most of the data. With my newly acquired iOptron CEM60 this is basically no longer an issue, so I wanted to see how much I could improve upon the old result by adding a lot of integration time. So here what I have obtained from a bit less than 30 hours of integration time: For comparison, here is the result I got back in 2015, which consists of
  13. Thank you! Yes, I use the Baader MPCC III. I get very noticeable coma without it, so a coma corrector is definitely a very worthwhile accessory, at least if you want to be able to use most of the field of view. I cannot comment on how the SW is compared to the Baader, as I've only tried the Baader. But I'm very happy with the Baader and I think it works really well.
  14. Thanks Miguel! That's right. The original field of view was quite a bit larger than the image suggests, but the overlap between the two data sets was not perfect. :)
  15. Hello everyone. Here is an image of M81 and M82 that I just completed. This is a combination of some data I captured three years ago and some that I captured a few days ago. Roughly 5 hours for each data set, so a bit less than 10 hours in total. The old data consists of 6-minute exposures with a quite dark sky, while the new subframes are 3 minutes and with more light pollution. I use a full-spectrum modded Canon EOS 1100D, and ideally I should use a UV/IR blocking filter to get correct colours. For the old frames I did not do that since I couldn't get a sharp image with
  16. Thank you. Yeah, I must admit I'm quite satisfied with this one. Now I'm eagerly awaiting the next clear night so I can shoot some galaxies!
  17. Thanks Richard. As a matter of fact, I was able to triple it. Had a good long night of clear skies the other day, so I got an additional 8.5 hours of exposure. Here is the result: (For some reason I prefer this orientation now...)
  18. Hi everyone. Here's an image of the Soul Nebula that I captured last night. It's the first image I've taken with my new iOptron CEM60 mount, and I love it so far. The guiding accuracy is a massive leap up from what I was able to do with my EQ5. This is also the first time I've remote controlled the imaging process, which was a very pleasant new experience (apart from the occasional technical glitch). Now I just have to build a robot that can set up the equipment for me, and this hobby will do itself.. I used my modded Canon EOS 1100D with an H-alpha filter and a SkyWatcher
  19. Hey guys, here's a quick update on the mount. After a lot of waiting I received the mount a while ago. I've been doing a lot of tweaking and experimenting with my new setup, but I did not get the opportunity to try it out properly before last night. I can say that I am extremely happy with it so far. It is very convenient to use and rock solid. The internal cable management is also a very neat feature. Here's a picture of the mount in action in the back yard, taken from my living room window. It's a 4-minute exposure, and the moon was almost full. The brightest star trail is Sirius:
  20. Very useful info John, thanks for sharing! I'm still waiting for my CEM60 to arrive (non-encoder version), but I'm reassured now that I've made a good choice. I'll be interested to hear whether your good first impressions persist as you get more experience with the mount over time.
  21. Sadly not yet. It had to be ordered from the manufacturer, and it looks like it won't arrive until late August. Let's hope yours arrives a little faster.
  22. Thanks Rob! I'll post some first impressions after I've received the mount and tried it a bit. ?
  23. Your setup looks absolutely awesome John! So the dovetail works as a hub for your cables? Never seen that kind of solution before.
  24. Thanks, Wim! Interesting to hear. To be clear, are you saying that the full payload including counterweights ends up at 25 kg, or that you actually need 25 kg of counterweights? I would think that the included 9.5 kg CW by itself should be able to balance up to 15 - 20 kg if put at the end of the CW shaft.
  25. Thanks, I think so as well. No doubt it will be able to throw around my SW Explorer 150PDS without breaking a sweat. ? I just got the regular non-EC version, which is supposed to have a 5" PE peak to peak. I think the 60% higher price for the encoder version is a bit much to justify the error improvement. Intuitively I wouldn't expect this difference to be very evident in the final images anyway, unless the exposures are unguided. Would be interesting to see some actual comparisons though..
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