alacant
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Everything posted by alacant
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Sorry, I'm lost. Could you explain where the f8 comes from? This wasn't a 130pds? Cheers and hoping you have another good seeing night.
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Superb. Persistent dew-forming-in-atmosphere haze all week here. Can't get anywhere near that clarity.
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Hi. I find the stars smaller with the pds, especially on longer snaps. On the refractor, the longer you leave it, the fatter the halos become. They're just simple doublets after all. Maybe I got bad lenses but it was poor by comparison. I sent it back, disappointed. It did however work out of the box; the pds doesn't. For me of course. YMMV. HTH.
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That image is becoming addictive. Amazing!
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Yes. They're Allen screws. I can't get rid of the tilt via collimation so I'm wondering if I could use them. Here's a light frame which shows top to bottom tilt. Focusing dead centre, it's too close at the top of the frame and too far at the bottom. I'm not sure how that relates to the sensor on my 700d. Or maybe I'm expecting too much...
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Hi. Yep. Will get out the matt black. Maybe the tube walls too... Not sure what you mean about the square of brass. The original tube didn't have one; it stops at a certain point when racking out anyway; puzzled!
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Thanks everyone. Done it. No protrusion. Perfectly round star halos right across an evenly illuminated field. As I removed the focuser, I noticed more seemingly undocumented screws around the focuser; the three sets of push pull screws at 120° around the barrel which look suspiciously like tilt adjusters. One set however cannot be accessed because it is directly beneath the focus knob. Anyone? TIA.
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- skywatcher
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Hacksaw?
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How much needs to be removed? TIA.
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cc comparison Here are my 2 markarian chains with different ccs solving to 648mm and 588mm respectively. Which is best for the 130? TIA.
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- skywatcher
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Hi. Thanks. Unfortunately not enough. Hence, I suppose the uneven stars and illumination on one side of the field. Other coma correctors retain the same focus position. SkyWatcher's not. Dunno. The design doesn't seem to have been thought about much.
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Hi again. OK, the next problem is the intrusion of the focus tube into the light path, especially problematical with the cc that sw seem to recommend. It looks like it needs around 2cm chopping off. Has anyone any guidelines? I'm thinking of a brute force and ignorance policy of removing the focuser and getting out the hacksaw. TIA
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Thanks. Yep. I think I've got it; camera hanging toward the ground and no shift. The adjustment seems to have done it. Just hoping it will hold in real life. I wonder if the tilt from the lock screw is associated with the maladjusted focuser? Thanks for your time and help.
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Hi. How was the coma at the edges? Did it tilt the camera? TIA. *Am almost there with the adjustment to obviate the need for the lock...
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Ah, OK. That's a good one to check. It seems fine no matter where the focuser is, but I use a Cheshire with cross hairs rather than a laser. I think however it should amount to the same end...
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Hi. Yes. I'm proceding according to these instructions. Nearly there...
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I think so. Would it collimate if it were not? TIA.
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Hi. Thanks. It's only a matter of time, trial, error and a few cloudy nights before I get the right combination of twisting and turning to get the focuser o hold! The main issue is that the focuser lock tilts the field. If I can take the latter out of the equation, I think the issue will have been solved. Until...
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Hi. Thanks for the link. Yes, it looks like that on the right of the image. That's why I think the focusing lock is tilting the field. That discussion was for field flatteners on refractors. Does the same apply to coma correctors on newtonian reflectors?
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Hi everyone. Here's a light frame with the field deliberately tilted with the focus lock screw. It's distorting the stars, but not producing coma. Strange. This much tilt on my faster f3.9 and it would be coma city. Does anyone know what this effect is called? TIA.
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Hi. Yes, a Cheshire is all you need, one with cross hairs is even better. There are a lot of idealised diagrams in the guides which look nothing like the real thing. Here's what it actually looks like through a 130pds looking through the focuser with and without the Cheshire. 1. Get the secondary more or less centred just by looking at it. 2. Insert a Cheshire with cross-hairs. 3. Use the secondary screws to make the cross-hairs intersect with the centre of the of the primary. 4. Adjust the primary to centre everything else. 5. Now go out and look at an out of focus star. Adjust the primary again tiny amounts to make it circular. Forget all that. Just make it look like this:
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Hi. I had a go at the tension but unless the telescope was pointing overhead, still couldn't get it to stop slipping . Even the slightest turn on the lock screw -not even trying to lock anything- and it tilts. You can't see it so much in a stacked image, but here's a light frame from the same; alas with the lock screw tightened...
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Hi and welcome. It's easy. As soon as you get to do it on a telescope, you'll see it's intuitive and will wonder what all the fuss was about. Some guides make a simple one-minute task seem horrendously difficult. So have a quick Google, but don't read too much about it before you try! FWIW, I already had a 200mm telescope and got the 130mm because of the wider field of view. If you have a choice of which to get first, I'd recommend the 130mm. Good luck and clear skies...
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Excellent. I think you ought to write the pds guide for removing the out of box nightmares. Yeah. Even more surprised. They don't seem to have anyone on the ground, in the cloud or anywhere. If I have a problem with my Bresser, I send an e-mail to ES and they get back to me that day. Maybe I'm not comparing like with like but SW don't seem to do it like that(?). Anyway, it's clear again tonight so I'm gonna stop feeling sorry for myself and go and take some snaps!
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That's the problem; tighten it and it tilts the focus tube and/or changes the focus. The only way I could keep it flat was by trial and error between adjusting the two screws which hold the camera-cc combination in the focuser tube to 'anticipate' the tilt before I turned the locking screw. Am going to try your adjustments to see if I can get the focuser to hold without having to tighten the lock screw. Thanks for posting. There is hope...
