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Everything posted by narrowbandpaul

  1. Hi Steve Be wary of judging noise just by looking. It's an unfair test. Better is to take an area of the background and measure the standard deviation in a raw image. This is the noise in DN (ADU). Even this is not fair. The only real unit is the electron. To convert DN to electrons you can approximate with e/DN=Well capacity/Saturated Pixel Value. Well capacity you can get from the camera specs and for the saturation level look for a saturated star and measure the peak brightness. Then noise (e)= (Well Capacity/Saturation)*Std Dev If the noise is around the quoted value for read noise then
  2. Hi guys. Thanks for the responses. Obviously the major thing left out was background noise. This only adds shot noise and so if you are background limited then either method will result in similar stats. It's nice to have consensus agree with the maths. Kinda confirms you're doing the right thing. Clear Skies.
  3. Hi Guys I have done some analysis of this subject. Thought it was useful so I typed it up so that others may benefit. It addresses that age old dilemna of whats better: A few long subs or may short ones. Some might be surprised others won't be. Hope it is useful and sheds some light on the topic and enables us to get better images. Paul Influence of Read Noise on SNR of multiple images.pdf
  4. If you are just visual then surely the 2.5" would do the trick. Are you using bino viewers or any other heavy accessory at the back of the scope. I think I have only ever really seen each scope with a starlight focusser so I can't really comment on the stock one. It can't see it being unsuitable. As I said they are both excellent scopes and I remember the diffraction pattern through the 100 f8 as being textbook. Each scope will be slightly different of course. The 115 was also really good though. It's a tough choice!
  5. The description of the scopes sounds like its TMB's you are thinking of. I have looked through both and they are both excellent. In visual astronomy aperture does win. Both scopes have roughly the same overall length. If your mount can take 115 then you have both more aperture and a brighter image (f7-f8). Either will not disappoint if you are thinking of TMB's paul
  6. Stuart, Sounds like there is no place in this world for theorists. There wasn't any mention of the scope used as for a fair test of a camera and sub length that would need to be the same. You dismiss science out of hand without seeming to know how it works. There have been many theorists who have made great contributions. Einstein was one. Without GR corrections to time intervals GPS would not exist. Period.
  7. Came across this phenomenal image of Centaurus A radio galaxy. It's 120 hrs of LRGB. The image captures several things for the first time by an amateur. It's an amazing image and the imager requires a round of applause. heres the link.... http://www.rolfolsenastrophotography.com/Astrophotography/Centaurus-A-Extreme-Deep-Field/29643205_8ZwvgW#!i=2536914799&k=mNgSprP Enjoy!
  8. This is an article by Richard Crisp- he began the Narrowband technique amongst amateurs. He is also a scientist. This is a mathematical view of the issue, graphs included! hope it is of interest Paul http://www.narrowbandimaging.com/images/exposure_equivalence_crisp_04162008.pdf
  9. What a fascinating discussion This is a perennially discussed topic amongst imagers it seems. With a physics background I thought I would add my view in here as well. Firstly in defence of science, not that it should need defending, the theory behind the SNR of an image does take in to a whole host of factors- things like read noise, shot noise, dark shot noise, dark fixed pattern noise, light fixed pattern noise, background noise, telescope efficiency, QE, filter transmission, elevation of target and seeing (I posted an article on this several years back). Some of these a easily measured, som
  10. It's a very nice scope, but is this a review?
  11. Per, You will need to eliminate as many variables as possible, which will be a tough task. An experiment under stars may produce some results but the differences between the various models might be so small as to be masked by random variations. Still, a practical demonstration would be interesting reading. Paul
  12. Cracking images as always Mike! Jealous of your location in the Southern Hemisphere.
  13. The only fair test is a scientific one. There is too much ambiguity in testing under the stars. You would need the object at the same elevation, same background light pollution, same amount of atmospheric extinction. There are so many things you can't control that the test would be meaningless. The photon transfer is a less exciting way of doing it, but it's the only fair way unless all cameras are tested on the one night from the same location. I have a photon transfer analysis of the ML8300 but its not my camera so can't really post the results. Hope that helps Paul
  14. If camera testing is your goal then the fairest way of doing it, as opposed to testing it on the sky with the vast number of uncontrollable variables, is to perform a Photon Transfer and Dark Transfer analysis. This will give you numbers like the Gain, Full Well, Read Noise, PRNU (photoresponse non-uniformity), DSNU (dark signal non-uniformity). These properties will allow you to tell how a camera will perform to any given scene. Comparing cameras on the sky is fraught with complexities that would render a meaningful comparison void. Good luck.
  15. Very nice Gordon! How is life with the PL16803? Paul
  16. I don't know where the 20K ADU mantra comes from. The quality of your flats is dependent on the total number of electrons used to calibrate the flats. Ie the number of electrons per pixel times the total number of images taken. Surely you would want to maximise both terms by using more like 2/3rds of full well (~40K ADU). There might be non linearity effects but these should not even manifest themselves at 2/3rds full well. CCDs are very linear devices, it's one of their strong points. I can't see any reason to use less than 1/2 full well. I could of course be missing something, but this is m
  17. Hi all. The [OIII] line is in general much weaker than Ha. I don't know of any cases where it outshines Ha (though I stand to be corrected). This will invariably lower the signal you receive and hence lower the Signal to Noise ratio. Secondly if shooting in moonlight then you will still receive some background flux passing through the passband of the filter. It is unarguable that the emission line filter will lower the amount of unwanted signal compared to a broadband filter. It won't remove it though. This background signal will increase the noise in the image, further degrading the SNR. When
  18. i posted this a while back, think it sheds some light (pardon the pun) on the issue raised by davew... http://stargazerslounge.com/astro-lounge/77512-focal-ratio-vs-aperture-size.html
  19. Ainsley, a 12" dob will show you much, especially from a dark site. since you want a big dob, I would look at 12"+. Beware...they are big and a bit cumbersome. If thats OK for you then go for it. For observing, aperture and dark skies is king!
  20. the mesu200 is better than say the paramount? If that is so wouldnt it be used instead of the paramount, which costs more than 2x the price. For 5000euros it might be decent value for money, but to label it the best mount bar none is outlandish. Unless of course you have used every other high end mount...... dont suppose you work for mesu or whoever make the mount? dont post opinions as if they were fact....thats misleading
  21. Paramount ME, AP1200, AP900, GM4000, EM200. I seen all but the GM4000 in action. All lovely mounts. The Paramount and the GM4000 would be observatory mounts whilst the others could be classed as portable also. Although the AP900/1200 would be a bit awkward. The RA axis splits in two for the AP900 and I assume for the 1200 also, which is why these can be classed as portable. All these mounts would be fine permanently mounted. all these will cost a few pennies.
  22. the red is oxygen, same as the usual green colour. The red exists higher in the atmosphere, as this emission involves a very long lived state that only exists in very low pressures/densities. The blue may very well be nitrogen, it is rarer I believe to see Nitrogen during an aurora. Where abouts are you in the highlands.... will check to see if there is any clear sky here in stirlingshire.
  23. if you want an AP mount the AP900 is hard to beat. after all your thread title suggests you are after an astro-physics mount.
  24. stars look a bit soft, im thinking your focus is a bit off....
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