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johnha

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Everything posted by johnha

  1. Hi, Many years ago I read that you could use the 'sunny 16' rule with the moon. This basically states that in full sun (as the illuminated part of the moon is) you should use f16 and the reciprical of the ISO as the shutter speed (i.e. at ISO 100, 1/125th @ f16 and at ISO 400, 1/500th @ f16). Whether this still works through a scope I don't know, if it does, then at ISO 100 you'd have 1/250th @f11, 1/500th @ f8 and 1/1000th @ f5.6, maybe?
  2. Yes 500/8 works the same for camera lenses, although there's usually a variable diaphram to control the aperture (but not in the case of a mirror lens). Correction, the front element is 82mm diameter, I presume the aperture is masked down to 62.5mm at some point. John.
  3. Hi All, I have a 35mm photo mirror lens (Tamron SP 500mm F/8 82mm front element) and a 10mm eyepiece convertor for it. From a quick look on the web it looks like it may be of Klevtsov-Cassegrain design. When new this was several hundred pounds worth of camera lens. I have used it on and off as a 'scope, and when comparing it to my 4.5" newtonian at 45x the image quality has been very similar. Has anybody compared something like this to a typical compact 80mm scope or have an opinion on such a comparison? Obviously it isn't as versatile as a dedicated scope (and lining it up without a finderscope is tricky). I'm using it on a standard photo tripod/ball head as I can't attach it to my EQ2 (I presume there will be an adapter to do this?). Lens details: Tamron SP Adaptall-2 500mm F/8 Model 55B Thanks, John.
  4. Hi, For me the most important thing would be to try to get one which goes up high enough for a comfortable view (which may be above your eye level). John.
  5. Another update: Correction, I can focus the 25mm eyepiece after all (don't know what I was doing wrong last night). Also the 6mm is probably too much for the 'scope. They have made a huge difference and really boosted my interest now I have several magnifications to use. John.
  6. Update: I now have the eyepieces, Meade MA series 25, 20, 17, 12 & 6mm with a 0.9 moon filter. There is a definite improvement comparing the 20mm with the original 20mm and the eyecups also help. I don't have enough focus adjustment for the 25mm (could have guessed this had I thought about it enough). Only tried the moon and Jupiter so far but overall very pleased with them. John.
  7. Thanks for the input: Swamp Thing - I'll have a look at the finderscope and see if this is the case. I have definitely decided not to upgrade it, I'll see what difference the eyepieces make. Kenmyers - Happy is a relative term! I guess I'm pleased it still works after a long time in the loft, after I've used is some more I'm sure I'll want more/bigger/better. Having spent more time with it I think the mount is probably going to be adequate for now. As for aligning it, I've managed this reasonably well but I'm far from proficient at it at the moment. I glimpsed the nebula through clouds tonight but it had clouded over before I got home. On the plus side, I've done a bit more research and am no longer interested in the small GOTO idea. I'll have a look at some dobs but I think I'll be looking at a 6" or 8" newtonian when I decide to upgrade. Thanks again. John.
  8. Thanks John. The Tasco came with the smaller eyepieces, but there's a blanking plate on the focussing tube (which I measured as just under 1.25" but I can't believe it won't be). For comparison I also have a Tamron 500mm 80mm f8 camera CAT lens with a 10mm eyepiece adapter which gives slightly inferior images compared to the Tasco with the 20mm eyepiece. If you don't have an EQ (indexed) mount, how easy is it to line a dob up? John.
  9. johnha

    Hello!

    Hi All, I'm John and I've just joined the forum. I have an old 4.5" reflector and couple of pairs of binos and a cobbled together 500mm f8 Tamron mirror lens with a 10mm eyepiece adapter to play with at the moment (looking to upgrade as soon as I know what I want). John.
  10. Hello, I've just joined the forum and I'm looking for advice on my old 4.5" newtonian. It is a Tasco 900mm f8 on what looks like a mount similar to the Sky-Watcher EQ2 with a wooden tripod. I've gathered enough info to know these aren't well regarded, however I spent the money a long time ago and what I've seen through it has been worth it. I understand the orignal eye pieces (4mm & 20mm) aren't great and have orderd a set of Meade ones (25m to 6mm) to get a better idea of the 'scopes abilities. I don't really want to spend any serious money until I get a better idea about what my interests are (split between planetary/deep sky at the moment) and how 'into' it I want to get. Having used it recently to view Jupiter I'm reasonably happy the tube/mirrors deliver sufficient quality to keep using it. But is this the right decision? Will it hold me back or frustrate me too much? I've managed to set it up reaonably well, requiring only slight adjustments to the declination to track Jupiter along the hour axis, but I'm assuming the mount isn't going to be useful to find faint objects not visible to the naked eye (the finderscope isn't great either). There is also considerable 'play' in the gearing which doesn't help. I am considering replacing the mount for a better one, would investing in this be better than replacing the 'scope? On the other hand, would I be better starting from scratch and getting a good starter scope & mount? The main reason why I haven't used it much is the bulk/aggro of setting it up, and some of the £3-400 compact GOTO 80mm are starting to look interesting, but I'm wary that I may regret the investment later? Obviously I'm waiting for the new eyepieces to arrive and clear skies to see what I've currently got, but any comments or suggestions would be very welcome. John.
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