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symmetal

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About symmetal

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    Proto Star

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    North Cornwall
  1. Ooh! that's a bit worrying Dave. I wonder if FLO can send them to Es Reid for checking/fixing like the other WO scopes. Alan
  2. Thanks Dave, Clear Outside shows 5 green nights coming up so I thought I got the RC just in time. Alan
  3. Yes it's a real pity Dave having waited so long. Now writing email to FLO. It's back to using the WO-61 then for the ASI1600. At least it's now much better once I got the tilt sorted out. Alan
  4. You do agree it's a fault with the scope then Dave and needs returning. Alan
  5. FLO. Have you tested yours from FLO yet Dave?
  6. Took my first image with my new RedCat-51 this evening. Bahtinov focusing was very precise and easy. I used the ASI1600MM with filter wheel and took this 45 sec L sub centred on the Christmas Tree Cluster. Look at the bottom of frame particularly Bottom Left, out of focus smeary stars. I took three more subs rotating the camera through 90 deg each time and the horrible stars corners rotated 90 deg each time so looks like the fault is with the scope. I've included two CCD Inspector images of the 0 and 90 deg images which shows it clearly. I thought Petzval scopes were meant to save you having to bother with spacing and tilt troubles. Do you agree it has to go back? Alan
  7. Hi Andrew, I got the reasoning from the multitude of posts on CN where they can get a bit obsessive about the ASI1600 and noise. The background sky glow limits the faintest detail you can get from the target. Increasing the exposure duration beyond the point where the read noise is masked by the skyglow won't yield fainter detail and will give more overexposed stars due to reduced dynamic range which is the main reason for not exposing longer. The shot noise from the intended target isn't distinguishable from the shot noise and light pollution 'noise' from the skyglow and in light polluted skies the skyglow noise is much more dominant. In very dark skies there would be an advantage in taking longer subs as the target shot noise contributes more to the overall noise. RGB imaging in moonlight gives very noisy images with the overall light pollution 'noise' being dominant over any target noise. Stacking more shorter subs should give noise reduction similar to stacking fewer longer subs (same integration time) when you're skyglow limited. That's my understanding, and I'm not a noise 'expert' and am willing to be proved wrong. Alan
  8. I would like to purchase it Stu and can pay by bank transfer. Alan
  9. I don't think the talk indicated that long exposure imaging is dead, but seemed to confirm the reasoning (that I've mentioned in the past ) that there's little point in exposing beyond the point where the sub sky background swamps the read noise. For really dark skies, even with CMOS, this still means exposures of several minutes or more and it's only in badly light polluted skies where exposures around of around 20 to 30s are considered 'optimal'. The formula I use is where the sky background reaches 10 * RN^2, (that is 10 * (Read Noise squared)), which fits in nicely to the equations at the end of the talk before he skipped all the gain related info. For my ASI1600 at unity gain and offset 56, 10 * RN^2 = 1386 ADU which is what I aim for. For my rural skies this equates to 45s for L, 120s for RGB and a lot longer for Ha. Actually to get 1386 ADU for Ha takes over an hour so I usually stick to 600s Ha as a compromise. For my Atik One 6.0 CCD, 10 * RN^2 = 1226 ADU (estimated offset) which equates to around 240s L, 600s RGB and almost forever for Ha. I limit Ha to 1200s usually. The talk graphs indicated stacking 1200 5s exposures won't give you a similar image to stacking 20 images of 300s (same integration time), as cameras aren't 'perfect' and there is a significant minimum exposure time that is necessary, even for CMOS. So I think I'll continue as I have been doing. Alan
  10. From the M48 thread the focus distance is 59.7mm. You can remove the adapter piece with the M48 thread to expose the M56 mounting thread. The focus distance from the M56 thread is 77.7mm. To remove the adapter, looking from the rear there are three grub screws in the centre of the 3 cutouts on the M48 adapter. Loosen these grub screws and the adapter unscrews. You will probably have to tighten the rotation lock screw first. WO only do three camera adapters from M48 for Canon, Nikon and Sony. I forgot to order the adapter with the scope and tried with an M48 to T2 adapter first but couldn't reach focus with my Canon. Have the M48-Canon adapter on back order. It may be easier for you to adapt from the M56 thread as there is more room to play with if you can find the right adapters. Alan
  11. I don't use light pollution filters so can't advise. One review on FLO of the Neodymium said they couldn't correct the colour cast when used for RGB imaging. It's mainly intended for visual I believe. Hopefully someone else can offer some help. Alan
  12. Vlaiv has pretty much said it all. If you look at the histogram curve of your image frame, (lights, flats, darks or bias), adding offset shifts the whole curve to the right, while reducing offset shifts it to the left. On the settings panel of some cameras 'offset' is labelled as 'brightness' but it's the same thing. Astrophotography processing generally involves stretching the dark areas of the images quite a lot and this is where the majority of the noise also occurs in the image. The darks and bias are used in calibration to help reduce the amount of noise present. If any frames have pixel values of zero it's highly likely that image data has been clipped, and then the calibration will not be applied correctly as the noise distribution in the frames is not representative of the true noise present. Adding a constant offset value to your frames avoids this situation happening. Like vlaiv I found the offset values often quoted for the ASI1600 are not high enough and you get some black level clipping. I've found an offset of 56 at unity gain just avoids this. It's worth mentioning that the ASI1600 (and possibly others) actually clip to a value of 1 and not 0, (well mine does anyway). This means that the minimum output value is 16 and not zero (when converted from 12 to 16 bit resolution). So values of 16 are most likely clipped values. At an offset of 56 the minimum value I get is 48 (16 bit) which is a value of 3 from the 12 bit A-D converter. So that's just OK. Alan
  13. If your only taking mono (luminance) images then I would have thought the Neodymium would be fine to use. Here are the responses of the two. The UV-IR rejection of both of them is similar, the Neodymium cuts off at 700nm while the UV-IR cut off is around 680nm. The Neodymium is a light pollution filter too so also cuts a lot of yellow and some green. This would give quite a severe colour cast to RGB images but have little to no effect on luminance images of the Sun and Moon as far as I can see. Neodymium UV-IR Cut Alan
  14. DHL delivered this from FLO yesterday. Was going to try it out during the day with the DSLR but being M48 rear it doesn't fit the standard T2 adaptor. In too much of a hurry ordering it to read the fine print. Tried with M48-T2 adapter but couldn't get focus. Ordered WO M48-Canon adaptor from FLO but they're currently out of stock. Will try with ASI1600 and filter wheel during the day as nothing to see at night at the moment. Alan
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