#21  
Old 07-07-2013, 09:26 AM
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DavidTrap (David)
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Here are the links.

Images are centred on the pointers - with the southern cross at the top of the frame (half missing at 24mm)

I'm mainly posting these so you can pan around and see the peripheral distortion. The 24mm frame was shot at Bin2x2, so is smaller.

14mm

24mm

Hopefully what I've discovered about back focus being affected by CCD filters will help some of you in the future if you decide to try zoom lenses on your CCD camera.

DT
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  #22  
Old 07-07-2013, 12:24 PM
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alocky (Andrew lockwood)
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Thanks for posting these David. They're better than the stars at the edge of the full frame image flat out at 14mm and f2.8 (unsurprisingly!), but I wonder how many stops you'd need to lose before they tightened up? Also, I can't sure why a prime lens would be be less sensitive? If anything, the rays from the outer edge of the rear lens element to the sensor would be more critical as the lens is shorter? (Not a great deal of thought put into that, first order thinking only!)
Still - a new front cover and lens mount for the QSI ain't exactly cheap. hmmm.
Thanks again for leading the way!
cheers,
Andrew.
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Old 07-07-2013, 04:18 PM
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DavidTrap (David)
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Thanks Andrew,

The 8300 chip is significantly smaller, so it should be better than the FF chip. I'll have to do some test shots on my D800 and see how it compares for myself - might be whinging about nothing!

Link - this is a shot taken with an 85mm prime lens mounted on the CCD (before I'd made the bracket though). The stars are much tighter in the corners.

I was presuming that the focusing mechanism would move lenses inside relative to one another. Given that I was focusing on an object at infinity when the focus distance scale was reading 0.3m would mean that the optics wouldn't be where they should be to produce sharp focus across the field of view. I guess the prime lenses might suffer the same fate, but I hadn't seen it with the 85mm lens. I wonder if the 14-24mm lens is such an extreme case that it is more sensitive to a slight change in backfocus. I had the lens stopped down to ~f4 - an imprecise science given the lack of an aperture ring.

Last edited by DavidTrap; 07-07-2013 at 04:23 PM. Reason: added a bit
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Old 07-07-2013, 05:27 PM
cfranks (Charles)
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That is a really brilliant image David! I'm trying to get enough subs of the same nebula but I'm using Pentax 6x7 Prime lenses on my 683 and they seem a bit softer than your lens. I'm trying a 105mm and 150mm and have a 75mm waiting to go. Your image gives me inspiration!

Charles
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Old 07-07-2013, 05:54 PM
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Thanks Charles - I nailed the focus that night, evident by the diffraction spikes from the 9 blade aperture diaphragm!

DT
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Old 07-07-2013, 09:07 PM
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Yep - that's a superb Antares shot. I think the 14-24 does an amazing job, but, as you say, it's a pretty extreme bit of glass. The 8300 chip is pretty close to a crop sensor size-wise, I wonder if the lens correction in photoshop would be close enough if you told it you'd used a d200 or similar? It certainly improves things with the full frame.


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Originally Posted by DavidTrap View Post
Thanks Andrew,

The 8300 chip is significantly smaller, so it should be better than the FF chip. I'll have to do some test shots on my D800 and see how it compares for myself - might be whinging about nothing!

Link - this is a shot taken with an 85mm prime lens mounted on the CCD (before I'd made the bracket though). The stars are much tighter in the corners.

I was presuming that the focusing mechanism would move lenses inside relative to one another. Given that I was focusing on an object at infinity when the focus distance scale was reading 0.3m would mean that the optics wouldn't be where they should be to produce sharp focus across the field of view. I guess the prime lenses might suffer the same fate, but I hadn't seen it with the 85mm lens. I wonder if the 14-24mm lens is such an extreme case that it is more sensitive to a slight change in backfocus. I had the lens stopped down to ~f4 - an imprecise science given the lack of an aperture ring.
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Old 07-07-2013, 10:18 PM
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Quote:
Originally Posted by DavidTrap View Post
Thanks Charles - I nailed the focus that night, evident by the diffraction spikes from the 9 blade aperture diaphragm!

DT
It was the diffraction spikes I noticed. Superb. I use @Focus2 (TheSkyX) and they don'y come out anywhere near as sharp as yours. I put it down to a 'soft' or 'Portrait' lens. Did you just keep tweeking the focus or do you have a secret recipe?

Charles
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  #28  
Old 08-07-2013, 05:27 AM
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DavidTrap (David)
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Andrew - tried lens correction in Lightroom and it just moved the smears outwards, but didn't tighten the stars.

Charles - It was focused with a Bahtinov mask from a 4 inch 600mm refractors balanced precariously ontop of the lens - produced a very fuzzy diffraction spike. Just got lucky that night!

DT
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  #29  
Old 11-07-2013, 12:16 AM
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Looks good, David! When I was researching CCDs, I noticed that many other manufacturers (QHY, Atik, SBIG, etc) have followed QSI's lead in offering mono camera + CFW options that fit within DSLR lens back focus requirements.
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  #30  
Old 11-07-2013, 10:58 AM
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ZeroID (Brent)
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Just harking back to an earlier post in this thread. I have heaps of stepping motors lying around at home ( and more available ). All 'rescued' from copiers and printers being dumped at work. A lot are brand new from unused accessories or modifications. Many also have the driver board attached or built on. I can normally get with plugs and some wiring as well.

If you want to provide pix or info of what is suitable for your project and are happy to cover postage across the ditch I could supply a few DIY tinkerers out there. Happy to maybe swap for other bits I might like, filters, another diag, you name it.

This offer is to anyone following this thread of course. PM me or post here. I can send pix of available bits.

Also got some small DC motors, some with gearboxes and quite low ratios, screw drive miniature motors ( slow, no backwinding).
Optical sensors, some microswitches.

Hmm, I should be building a 3D printer ... I've got shafts and gears and other stuff.

Anyway, anyone interested, give me a yell.
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Old 11-07-2013, 04:46 PM
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DavidTrap (David)
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A very generous offer Brent,

I suppose one issue may be that I'd prefer a motor to interface to a computer so I can use Focusmax for automated focusing.

DT
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  #32  
Old 12-07-2013, 05:59 AM
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ZeroID (Brent)
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David, some of these motors already have interface boards attached. They accept standard digital data as per any computer will output. Otherwise buy commercially available driver boards. I'm just offering the motors, they can be quite expensive $50 + probably and I get them for free so share the bounty. I won't ever use them all.
As I said I have small DC 12v, 24v and I think 5v as well. Some with gearboxes and reduction systems. I may motorise a focusser or two one day but I've still got motors to burn.
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