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Sigma Apo 70-300 F4-5.6

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#1 Hilmi

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Posted 29 January 2013 - 09:21 AM

I'm considering getting the above mentioned lens as a low cost solution for DSLR imaging on my Vixen Polarie, is it any good for astro-photography? This will be the first time I buy a camera lens with the express aim of using for this purpose and I am looking for some advice

#2 orlyandico

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Posted 29 January 2013 - 09:47 AM

its a consumer zoom. i think the canon 200 2.8L is a better choice.

#3 mmalik

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Posted 29 January 2013 - 10:17 AM

This... thread may have some useful info; not an exact answer though. Thx

#4 Ron359

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Posted 29 January 2013 - 12:17 PM

I've had one. Its a good lens/value for daylight photos but really too slow for astronomy at its f/5.6 300mm f.l. that needs to be stopped down further, if thats what you intend. And being a zoom, its quality for astronomy is not 'the best'. If you want to start out in piggybacking long exposures for not a lot of money, and if you're shooting with a Canon DSLR(?) I'd recommend the Canon 50mm 1.8 lens (stopped down to 2.8). Its inexpensive and decent fast optics for astro. HTH Ron

#5 Hilmi

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Posted 29 January 2013 - 12:29 PM

Im looking for a light weight longish focal length for the polarie. A for allmy sserious stuff I use my sct or televue 60is. I already have the 50mm for very wide angle work

#6 Ron359

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Posted 29 January 2013 - 03:08 PM

What about a 180mm f/2.8 ED Nikon? - Almost as long as the Canon 200 2.8 but much cheaper. With Canon adapter they make great astro lenses. There is even one posted on CN now:

http://www.cloudynig...ct=73302&sor...

Its not mine, and I wouldn't sell mine. Well, maybe for the right price. :smirk: Ron

#7 dp297

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Posted 29 January 2013 - 03:37 PM

Or here for another Nikon 180ED

http://www.astromart...ified_id=808853

#8 ky1duck

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Posted 29 January 2013 - 05:43 PM

- dont have the 70-300 but i have the 200-400 f4.5/f5.5 sigma apo like it use it with my canon t3i. test pic i took with it


Posted Image

10 90sec @iso800 and 11 @ iso 400
the 16 point stars were a little strange tho(but cool looking)just my 2 cents

robert

#9 pfile

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Posted 29 January 2013 - 08:53 PM

the canon 200 f2.8/L really is a great lens, so i second that recommendation.

dslr shots:

Posted Image
Posted Image

the above are stopped to f/4 with the internal diaphragm.

ccd shots (wide open @ f/2.8 with 5nm Ha filter)

Posted Image
Posted Image

#10 mmalik

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Posted 29 January 2013 - 09:05 PM

I am for smaller APO... over lenses for wide angle AP; sort of middle of the road between too wide lenses and too narrow scopes. Thx

#11 Hilmi

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Posted 29 January 2013 - 11:52 PM

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.

#12 Samir Kharusi

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Posted 30 January 2013 - 03:41 AM

Rather than going in blind, I would suggest some homework first, so that whatever purchase you make eventually is guaranteed to work. What I would do, step by step:

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:

f2.0: 30sec
f2.8: 60sec
f4.0: 120sec
f5.6: 240sec

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.

#13 Hilmi

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Posted 30 January 2013 - 04:35 AM

Simple enough method of figuring out the type of lens. I am worried about trying it because it is 1.5 Kg above the optimistic load limit of the polarie. I will try this experiment with my kit lens instead. When I was looking at the Sigma, I was thinking of using it at 150mm, which from all accounts I found online seems to be about the maximum practical focal length for the Polarie.

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.

#14 fishonkevin

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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.

#15 avarakin

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Posted 02 February 2013 - 09:04 PM

It is actually not a bad lens for AP. I bought it some time ago and took this picture:

http://www.astrophot...rica-pelican...

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:
http://www.astrophot...18-m24-m25.html

Alex

#16 orlyandico

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Posted 02 February 2013 - 11:39 PM

i have a lot of those ebay lenses.

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.

#17 avarakin

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Posted 03 February 2013 - 12:08 AM

Yes, I was using my Rikkenon stopped down to 5.6 which is not bad - it is similar to most of the scopes. Image quality at F4 is also not too bad but I do not want to take any chances, so I just stop it down to F5.6. Interestingly the lenses I have normally do not suffer from CA wide open, instead they just have some kind of coma and spherical aberration.

Alex






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