Sigma Apo 70-300 F4-5.6
Posted 29 January 2013 - 09:21 AM
Posted 29 January 2013 - 09:47 AM
Posted 29 January 2013 - 12:17 PM
Posted 29 January 2013 - 12:29 PM
Posted 29 January 2013 - 03:08 PM
Its not mine, and I wouldn't sell mine. Well, maybe for the right price. Ron
Posted 29 January 2013 - 05:43 PM
10 90sec @iso800 and 11 @ iso 400
the 16 point stars were a little strange tho(but cool looking)just my 2 cents
Posted 29 January 2013 - 08:53 PM
the above are stopped to f/4 with the internal diaphragm.
ccd shots (wide open @ f/2.8 with 5nm Ha filter)
Posted 29 January 2013 - 11:52 PM
Posted 30 January 2013 - 03:41 AM
1. Attach your TV60is to the camera. Yes, it is too long focal length and too slow in focal ratio for the Polarie, but bear with me.
2. Polar align your Polarie as best you can. I am assuming that you already own the Polar Finder Scope? If not, then you are going into the wilderness.
3. Point at some bright starfield and shoot 5 subs each at 15sec, 30sec, 60sec, 120sec. Check what length of subs give you 4 well-tracked frames out of 5. This is your longest, good tracking limit at 360mm focal length (TV60is is an f6 if I recall correctly). Let us say, it is the set of 60sec subs. That means that the Polarie+your DSLR are good for 30sec subs at a focal length of 720mm or 120sec subs at a focal length of 180mm, etc. Simple inverse proportionality.
4. Now you are ready to choose what lens to buy, focal length and focal ratio. Just recall that you need the following minimal-length subs for the following focal ratios:
All the above are ball-park figures, but they do work. In the example above a good choice would be a 200mm f2.8 lens shooting 60sec subs with a yield >> 80% perfectly tracked. A 300mm f4.0 lens would be too slow because you will need 120sec subs. But a 300mm f2.8 requires 60sec subs and it will be fine, but costing $5k? Good luck and happy hunting.
Posted 30 January 2013 - 04:35 AM
I was also just looking at Jerry's list of good for astro-photography lenses and he recommended the EF 100mm F2.0 It's very reasonably priced brand new. If I could hunt down a used one, I have a feeling it will be even more reasonably priced.
Posted 30 January 2013 - 07:12 AM
Thanks for all the suggestions. I have decided to stick it out with the 17-85 kit lens that came with the 7D till I am comfortable with the polarie before moving on to longer focal lengths. First I will need to find a solution to the lens barrel creep, which is a big problem on this lens.
Hilmi, try using a rubberband or one of those Charitable Event wristbands that they give for a small donation.
Posted 02 February 2013 - 09:04 PM
I had to return it because auto focus had some mechanical problems. I am thinking of getting this lens again.
Another suggestion is to look for 135 mm lenses on ebay. They are very cheap and most of them are pretty good for what they cost. Of course this is a little bit of a gamble, but this way you can start a collection of lenses :-)
My favorite lens is Rikkenon 135mm F2.8 I bought off ebay for $20.
It is very sharp at F5.6, no visible aberrations. Here is what it is capable of:
Posted 02 February 2013 - 11:39 PM
a big problem is that they have eye popping levels of chromatic aberration.
the only camera lenses i've tried that don't have CA are canon L glass..
alex.. i think you were using the rikenon stopped down right?
hilmi, i expect the 100mm f2 canon to have CA wide open. you will probably have to stop down to at least f4 or f5.6 to get rid of it.
i've only tried one canon L lens - my 180mm - and it has no CA wide open. it has.. a number.. of other aberrations though.
Posted 03 February 2013 - 12:08 AM