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Tommohawk

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Everything posted by Tommohawk

  1. Well, here's the latest. I did a bit or reading up and discovered that the latest of the Tamron F2.8 300mm lenses (360B version) gets good reviews on a par with Sigma and close if not quite as good as the Canon. Difference is I got the Tamron in good order for a jot under £300, where the Canon is... well, lots more. So whether this was a good move remains to be seen. I'll post some pics as soon as I can. One other advantage of the Tamron is I can save some back focus by fitting an M42X1 type Adaptall mount, and fit a 42x1 internal and 48mm external adatper which will screw straight into 2" filter wheel - this saves the width of the Canon to CCD adapter ie about 14.5 or 17mm depending on type. Allowing for a 3mm locking ring this uses 3mm back focus, filter wheel is ~20mm, camera connector is 17.5 if connected direct which leaves me 3.5mm to play with for a total of 44mm. Does that sound OK? Next problem is this requires a 2" filterwheel where I probably only need 1.25", so starts to get expensive for filters. And to make matter worse, at F2.8 I may need spooky fast NB filters. So the next techy question please is, what do people think about NB for F2.8? The Baader F2 set are £499 which is a bit stiff. Any thoughts on this please? Can you maybe put a 1.25" casette in the 2" wheel?
  2. Hey thats nice, thanks for posting. I was going to ask if you're mono or colour, and where does your Ha filter go? Also, It looks like youre not using the Geoptik as a support, so how is the camera/lens supported? Using the lens support foot?
  3. I looked at other brands, including Samyang and Sigma, and surprisingly the Tamron 70-200 seems to de well in reviews. Noisy and erratic AF, but I don't need that. Non-weatherproof body, but plastic so less condensation maybe. Anybody have any expereince with Tamron lenses?
  4. Hmm good question! Looks like when you stop down you reduce lens aberation but introduce diffractive effect. See here: http://www.kenrockwell.com/tech/diffraction.htm Thats a bit of a random search return, and would be useful to see something specific to our field, but look like the answer is yes, on balance you lose resolution if you stop down. Mike I now realise there seem to be 3 variants of the 70-200. The pre IS, the IS , and the IS version II. So this probably accounts for the price variations, and looking at the review sites the latest seems to come out best.
  5. OK, well fingers crossed - be sure to post anything you shoot!
  6. Fingers crossed for clear skies - maybe you can post results when you get some. Forecast only showing lots of down here!
  7. Hi Mike. I'd have thought the zoom version would lose a little in performance, compared to the fixed focus, no? Certainly more versatile though. BTW a non IS 70-200mm F2.8 went on *bay few days back for £599. Bargain!
  8. ... the other obvious (well not to me clearly) drawback with this approach is that when I go back to my 200PDS or whatever I'd have to start over. I cant see Baader making 200mm filters!!
  9. Yes, agreed, I went in a bit of a circle there, but 2" filters would lose me all that lovely aperture, no?
  10. I'm thinking of filters for the EF 300mm which looks like a 77mm thread. Doesnt look like anyone makes these, and even the 2" NB set is pretty expensive, and I'd probably want LRGB too. The words "DIY" and "lashed together" are immensely appealing - but not sure how I could achieve this. Somewhere I have an old Cokin filter, though i think this is smaller dia. I see new 82mm Cokin filters on *bay are cheap as chips, but not sure where I'd get square NB filters that big. Baader do 65mm square for E845, so pretty stiff and still a bit small I think.
  11. Just a quick afterthought... Does anyone make filters which attach to the front of the camera lens? Would this work from a technical perspective?
  12. That's useful info - I had planned to be fast enough to work unguided where possible esp on holidays away, and then maybe use guide at home. Key point is OAG is problematic when working that far down the light cone - I hadn't though of that. Which Baader filters do you have? Looks like Baader do standard type and F2 high speed version. Still getting my head round the issue of matching Pixel size to FL, but looks like with 200 or 300mm lens I'm more at risk of undersampling, no?
  13. Look forward to seeing the final result, and envious that U have got any data at all in this weather. Do the individual subs look ok?
  14. OK thanks for that - I had no idea about all this! Which reminds me of another thing I wanted to ask - but I'll post separately about that cos it's well off topic.
  15. Starting from scratch with filters, but hoping for NB. Interesting what you say about problems using NB at fast F's. Will have to bear that in mind. Through the course of this I'm wondering if the F4 300mm might suit better, especially given the point about matching to CCD camera pixels. Would still be faster than a fast frac. Is the general view that the image from say a 300mm F4 Canon lens is as good as a dedicated frac, say an F6 with 0.8 reducer?
  16. You can say that again - last time out I had goto and autoguiding problems which I have yet to sort before I can get back to any imaging. Forecast is for more rain and wind all week... and that's kind of the point of all this. Trying to find a way of taking compact set-up off the Canaries or wherever.
  17. see below! And youd have to dismantle to change filters I guess.
  18. Thanks, looks like filters are an option but maybe only with a draw. Re the ideall CCD pixel size, I think I sort of follow the conventional thinking on this - but received wisdom seems to suggest an ideal FL of approx 200x the pixel size, or in the case of a 300mm lens, thats 1.5 microns. Well the Canon has a pixel size of 4.3 microns and of course is typically used at much shorter FL. Would the ideal Pixel size for a 50mm lens really be 50/200 = 0.25 microns? I must be missing something! OK thanks, thats useful to know.
  19. Hi Olly yes that looks just the job - the TS microfocuser I mean, not the Tak! Whats your thoughts on the Canon lens with filter wheel for CCD ? Is there space for a wheel? BTW I just tried to check the depth of the ZWO filter wheel and noitced they now have cooled ZWO ASI 174 on sale for $799. Bit off topicHas anyone ordered direct from ZWO - do we get hit for VAT etc?
  20. Well I intend to move to a mid-size cooled CCD/CMOS so that should minimise the problem. Talking of which, I now realise that getting filter wheel between the Canon lens and a ZWO or other camera will be tight or maybe impossible? It looks like Geoptik do a filter draw type option, but any chance of a filter wheel does anyone know?? Agreed that would be fast - but too long for cabin bag. BTW - could you do me a big favour when you have a moment? I'd really like to know some measurements from the 130PDS to help with my F4 conversion raytrace. Can you tell me the tube diameter, and also the stock focuser height at mimimum - measured from tube to top of black 54mm adapter. That would be really helpful. Yes everyone seem to recommend the TS microfocuser rings - yet another bit of kit! My Fuji HS30EXR camera has "soft" manual focussing and its horrible - the Canon must be better than that. thanks for the tip about the aperture rings - youd think the diaphram would be clear without that when set wide open.
  21. Hi and yes I really like the idea of the ASA reducer used in multiple F4 newts as you have, either home made or Boren Simon. Trouble is the 150mm is too large for hand luggage which is key to this. A 130PDS F4 with ASA option would be fabulous - but I cant source an F4 130, or even a mirror for a DIY job. Well that looks pretty convincing!! Didnt realise the Pleiades had so much going on!! Yes it does help thanks - more great images! Well, funnily enough I wondered about the F4 300mm - but I'm surprised the field isnt flat given its meant specifially for imaging. Is it really that different to the frac?
  22. Thanks for that, and am hurriedly reading up on "thirds" focussing! As you say, F4 still better than F6 or F4.4 with redducer. Is there a mid stop - say F3.5?
  23. My main interest is imaging DSOs currently with DSLR but probably moving over to cooled CCD/CMOS when funds allow. I've recently been looking at options for a wider field fast lens/scope, partly to be airline portable also to be superfast to make the most of any imaging time on holidays. My first choice is an F4 130mm newt - thread elsewhere on this - but given this doesnt seem to be available, was looking at a TS photoline 80mm APO. However, the Canon 200mm F2.8L is immensely appealing too, and quite a good price. F2.8 sounds great - would knock spots of an F6 APO (F4.8 with reducer) for fast imaging. But reading up on this most folk seem to advise stopping it down to F4. Seems a shame to have a superfast lens and then stop down - the lens is very highly rated, so whats the point of getting an F2.8 and using it at F4? I think the answer is that working with superfast lenses is likely to be problematic for fosusing at least so maybe better to prioritise the switch to cooled CCD. I guess the question is, would an 80mm APO outperform the Canon 200mm at F4 in terms of overall image quality? Thanks as ever for any advice.
  24. Tommohawk

    M101 Pinwheel

  25. From the album: M101 Pinwheel

    © TC2014

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