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ollypenrice last won the day on January 6

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About ollypenrice

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    Imaging, Cycling, Thinking, Literature, French culture, Mountains...
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    South east France, Lat 44.19N.

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  1. Ah, but the thing about Starnet is that you don't have to remove the stars and call it a day. You can remove them and put them back at a reduced opacity, which doesn't require the same signal strength as a full removal. I've only done limited experimenting but I put the stars back using blend mode lighten as a top layer in Photoshop. (Put the linear image on top of the stretched starless, choose blend mode lighten, and stretch the top layer to taste.) Olly
  2. That's a glory, Lee! The Samyang lens is a stunning asset to astrophotography. In conjunction with Starnet for star reduction it must be the definitive widefield setup. 90 mins with a 7nm filter is incredible. Olly
  3. The sub length question has been re-answered by CMOS cameras which work well with short subs. High read-noise CCDs do not. CCDs do, from experience rather than theory, benefit from long subs. Plenty of CMOS imagers are finding 300secs at unity gain to be effective. In the end the key number is the total integration time and even with the fastest setup known to man you will be scratching the surface with half an hour per filter. The fastest setup currently appearing regularly on SGL is probably Gorann's RASA 8 and CMOS rig. Check out his posts and integration times. Noise increases as the
  4. The very high end refractors have always been there. The outstandingly good budget ones, now plentiful, have not. This is the age of the affordable telescope so let's not get hung up on how expensive the high end stuff is. The real story is about how good the cheap stuff now is. And if you're short of cash, why go for a refractor in the first place? There are insanely good budget Newts available these days and blessèd be John Dobson for showing us how to mount them. The Apos and semi-apos debate is a bit of a red herring since 1) the difference is very slight, 2) the individual scope
  5. Currently you shoot at F5 and a focal length of 750mm. F5 is good. Any faster and you'll almost certainly spend a lot of time struggling to get it all to work. So is there something about 750mm that doesn't please you? Is it too long or too short? To my mind it's a slightly 'in between' focal length, a bit short for galaxies and a bit long for nebulae. (I used to feel this about a 1000mm FL a few years ago when pixels were larger, but small pixels have made a metre a good galaxy FL nowadays.) If you want shorter, then the small modern refractors are excellent, as is the ultra-short Samy
  6. I can't pretend to understand the over-correcting flats problem because we were once plagued by it using an SX camera/Nebulosity/MAC computer (none of them mine. I was just the man on the ground.) We never got to the bottom of it. The flats procedure is different for CCD and CMOS. With CCD you can shoot flats then use a master bias as a dark-for-flats. It will work fine. With CMOS you must make dedicated darks-for-flats at the same exposure settings as your flats. As I understand it bias are not useful in CMOS imaging. I don't think your final image tells us anything about the effect
  7. You can only damage the mirrors and corrector plate by scratching them or breaking them so, if you haven't done either (and clearly you haven't), then they will be fine. They cannot be 'slightly cracked.' Optimism! Olly
  8. As others have said, very few scopes cover full frame and a small apo is unlikely to do so. You'd need to check the corrected and illuminated circle which will need to be at least 44mm. Given the limitations of uncooled DSLRs and the cash value of a full frame CCD I wouldn't entertain the idea of modding one when you can get a far better cooled CMOS for a reasonable price. Modding DSLRs made some kind of sense when the alternative was expensive CCD but that's no longer the case. When you say, 'Will my images from a 61 APO be too small on a full frame ?' I think you may be falling in
  9. One of the many nice things about AP is that you can choose what your image is about. I would just do as you've done and post two versions. This applies to lots of targets: do we want Ha in a Double Cluster image? I do and I don't so I made both. I don't feel, in your case, that the stronger IFN detracts from the galaxies in any case. Very good image! Olly
  10. Just for info, in AP 'deeper' is generally used to mean 'fainter.' And another note: you won't want more focal length for M31. It is utterly enormous. Check out Gorann's recent rendition at 400mm in which he didn't quite fit it all in. When I did it at 530mm with a full frame camera I still needed to make two panels. For any chip of APSc size or above you will need a rear lens element of some kind. This can be in the form of a Petzval or Petzval-like scope design in which the rear element(s) are in the main tube, or it will take the form of a flattener on the drawtube. Some manufacturers
  11. You're right but the trick is to gather the cables together close to the camera and run them all to the mount end of the counterweight shaft, to which you attach them. from there they can drop down low and won't move too much during a run. I host six robotic setups and that's been working well for us. Flips are routine. Olly
  12. Let's start with a target which will fit on the chip at either F ratio. So... - We lower the F ratio as in terrestrial photography by increasing the aperture. Now all pixels, including the target's, get more light and exposure time is reduced. You have captured more object photons. This is not controversial. But... - Now we lower the F ratio by reducing the focal length, leaving the number of object photons exactly as before. We cannot get something for nothing. What we can do, and have done, is concentrate the same number of object photons onto fewer pixels, causing them to reach
  13. That's great. The professional data bringing in the dusty ring around the Ha is new to me. I'm often surprized by how rarely we see this wonderful and huge nebula in images. It has a fine structure and looks as if it's being swept by a westerly particle wind to my eye. Olly
  14. If ever you have a few very 'difficult' stars - and you will - there is another trick to try. Make a copy layer and apply, to the top layer, a fully feathered eraser large enough to cover the whole problem star and its bloat. Nothing will change because the images are identical in both layers. However, make the bottom layer active, open Curves, and put a fixing point at the nearest bit of background sky before the bloat. Add a fixing point below that. Now you can pull down the curve above these points, playing with its shape, till the problem star behaves itself! Olly
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