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Digiscoping problems

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Old Tuesday 14th September 2004, 16:48   #1
AndyC
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Digiscoping problems

I had my first go at 'proper' digiscoping yesterday at Rutland Water. As expected most of the images as only fit for the bin, but a couple of problems that I need some help with cropped up.

Equipment is Kowa 822 scope with 20x60 zoom - straight scope, non HD glass.
Camera is Coolpix 4500 with Eagle eye adaptor.

Firstly, some of the images show vignetting down the right hand side only- see attached heron picture. It was clearly visable on the LCD screen and could only be cured by taking the zoom to its longest setting. The adaptor was square on the eyepiece and pushed in as far as it would go. This problem only affected some of the pictures. The rest of the time the LCD screen was clear of vignetting at mid zoom settings.

Secondly, a lot of pictures are suffering from highlight burnout. I was using the spot metering in the camera and I would expect some over expouse of the backgrounds, but the effect seems a bit extreme. Should I be changing settings on the camera to compensate?

Sorry to go on at such length, but any help will be much appreciated.

AndyC
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Old Tuesday 14th September 2004, 17:03   #2
Ashley beolens
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RE the Vignetting problem, I do not know what adaptor you are using but the cause of this is usually the alginment of the lens, if it is one of the adaptors that only have 1 locking screw, this often shifts alignment of the lens from the centre of the eye piece, try loosening this locking screw! if there are more than one screw adjust them until alignment is better.

As for the burnout, try under exposing slightly, I usualy have it set to -0.3.

Hope this helps.
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Old Tuesday 14th September 2004, 17:17   #3
Lee Walker
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Hi Andy, I dont think I can help much here, with the vignetting, you say the adaptor is square on to the eyepiece so this is making me think that your camera lense is not parallel to your scope lense, ie very slightly off which is only visable possible at low to mid zoom range and is cancelled out at the longer settings. As for the burnout,I get this sometimes and usually stop down to compensate for this, (usually works). Otherwise my second plan of action is to take shedloads of images of the same subject and bin the crap when I get home and keep the good ones! (out of 50 images I manage to get atleast 1 or 2 good ones, only joking, not that many!). Anyway good luck with solving your problems. Lee.
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Old Tuesday 14th September 2004, 17:31   #4
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Hi Andy

From your photo it would seem that your digiscoping adapter is out of alignment with the eyepiece ,to correct the highlight burnout try turning the contrast down on the camera.Hope this helps.

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Old Tuesday 14th September 2004, 18:37   #5
IanF
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Hi Andy,

I agree with the above. The adapter needs to be centralised over the eyepiece, best viewed at no camera zoom and adjusted using the screws as best you can whilst making sure it's flush with the top of the eyepiece. I used to remove the rubber eyepiece cup from the zoom. I do wonder if you have adjusted the eyepiece zoom as well as this may put the adapter out of alignment. by the looks of it you have taken a shot through the edge of the eyepiece rather than the centre which causes more distortion. From my experience the centre of the eyepiece has minimum curvature and is less distortion free.

With my Kowa I got best results at 20-30x zoom. I think the non-Fluorite glass of this model will always give softish images and purplish whites, but really the Heron looks pretty good considering. Another solution may be to give one of the new lowered power eyepieces a go. I believe they are far more suitable for digiscoping as I found the 20-60x zoom a very narrow eyepiece to use, although excellent optically.

As regards the burnt out highlights then more usually I'll adjust the EV setting by -0.3 or -0.7 and even more on really contrasty subjects. If you can, try to use spot metering to expose for the highlights in which case you'll need less EV compensation - not ideal though as sometimes the rest of the shot comes out too dark. As a compromise I'd rather have burnt out hihglights than the rest of the subject far too dark.

A tip to avoid the burnt out highlights is to try to digiscope on bright but overcast days as the subjects are less contrasty giving more even metering. Sunny days can be a nightmare. They help with faster shutter speeds but can gives very contrasty results.
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Old Tuesday 14th September 2004, 18:49   #6
AndyC
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Quote:
Originally Posted by IanF
Hi Andy,

I agree with the above. The adapter needs to be centralised over the eyepiece, best viewed at no camera zoom and adjusted using the screws as best you can whilst making sure it's flush with the top of the eyepiece. I used to remove the rubber eyepiece cup from the zoom. I do wonder if you have adjusted the eyepiece zoom as well as this may put the adapter out of alignment. by the looks of it you have taken a shot through the edge of the eyepiece rather than the centre which causes more distortion. From my experience the centre of the eyepiece has minimum curvature and is less distortion free.

With my Kowa I got best results at 20-30x zoom. I think the non-Fluorite glass of this model will always give softish images and purplish whites, but really the Heron looks pretty good considering. Another solution may be to give one of the new lowered power eyepieces a go. I believe they are far more suitable for digiscoping as I found the 20-60x zoom a very narrow eyepiece to use, although excellent optically.
Ian,

Thanks for the info.

I've just been having another look at the adaptor. This is the Eagle eye type which has four screws. When I look at it now its easy to see the adaptor moving off centre when the screws are tightened unequally, so I will have to take more care when using the scope! I would agree with you about the eyepiece I have. At higher powers it does suffer from CA. I tried to use the lower end of the zoom range when I was taking these pictures, but of course the tempation is to use the long end to get a larger image. I will also try the exposure compensation to try to stop the burnt out highlights.

Lots more practise required, I think.

Once again thanks for your comments.

AndyC
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Old Tuesday 14th September 2004, 22:05   #7
iporali
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Quote:
Originally Posted by AndyC
I tried to use the lower end of the zoom range when I was taking these pictures, but of course the tempation is to use the long end to get a larger image.
Andy,
I am practically repeating what Ian just said, but I think it is worth emphasizing
If you use the zoom eyepiece for digiscoping, I warmly recommend you to stay at 20x and do the zooming-in with the camera (and not too much of this either). Here http://www.tvwg.nl/testrapporten/tel...telescopen.htm you find a test, which compares the Leica, Swaro and Kowa scopes with different eyepieces. In the eyepiece section they show how the eye-relief changes during zooming - revealing why the Leica and Swaro are often considered the best scopes (=have the best zooms) for digiscoping. You simply get more image area with a good eye-relief due to less vignetting. Otherwise the Kowa 823/4 (Fluorite) and the zoom are comparable to the very best. And as Ian mentioned, Kowa should have a new line of fixed eyepieces which were designed with digiscoping in mind - the 27x could indeed be worth trying (just make sure it is the new design, the old one has a VERY narrow field-of-view).

Good luck,

Ilkka
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