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Old 27-10-2018, 11:03 PM
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Astrofriend (Lars)
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Astrofriend is offline
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.

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.

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!

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?

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:

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:

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