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Old 27-10-2018, 11:03 PM
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Astrofriend (Lars)
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Join Date: Aug 2017
Location: Stockholm, Sweden
Posts: 235
Hi all,
What a lot of replies! Thanks a lot!

One thing I must say about advantage to have a camera lens with built in motor. It's very pratical when you control it from a smartphone. No vibrations and the motor is already there without extra cost. I recently started to use this remote controlling app, now adicted to it :-) This is only when I travel with the equipment, for permanent setup I have others.

But still, do I get better performance from a telescope, then lets say the Canon 200 2.8L ?

Most telescopes that I have looked at have about the twice focal length so there is a difference so it can't be compared directly.

@Greg,
I have a 3" focuser on my TS130 APO refractor, from the beginning it was equipted with a 2.5" field flattener with reducer, very sharp but didn't work at all with a full frame sensor. Now I have a 3" field flatter without reducing. Sharp all the way out to the corner and more. Almost no vignetting. Very satisfaid. So I will say that at least a 2.5" focuser but better with a 3" to be prepaired for the future.

@Rick,
The Borg intstruments has always faschinated me, but no of my friends have one and can't tell how well it perform. Let us know when you get it delivered!

@Peter,
Yes! But can I use it at f/2 or do I have to set it down to f/2.8 or f/4 when using full frame to have it under control for shaprness and vignetting? Anyone used it for astrophotographing?

@Skysurfer,
Maybe I one day by that Canon 200 f/2.8L lens. It could be very interesting to see a full frame master flat from a lens like that, with different apertures, f/2.8 and f/4. Very interesting to see your astrophotos with the zoom lens.

Once I had the Sigma APO 70-200 mm f/2.8 zoom, it was very sharp, almost as good as my Sigma APO 150 mm f/2.8. But it was of a older design, maybe not the optics but the electronics that control it. It had problem with digital cameras. It was heavy, but with that lens I only had to brought with me one lens, very pratical. But my mind say to me, don't use zoom lenses for astro, in this case I was maybe wrong.

This is a lens that I for many years had have thoughts over to buy, the Pentax 67 300 f/4 ED lens:
https://www.pentaxforums.com/lensrev...m-F4-Lens.html

I don't get the focus motor then and the motor is something I'm today appreciate a lot.

Now I'm very eager to do a test with my Pentax medium format lens. Not for the sharpness, more other aspects that give me more experiences for the future.

I have added more text and photos about my vignetting test here:
http://www.astrofriend.eu/astronomy/...vs-pentax.html

/Lars
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