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Good targets for a 100mm lens?

Ags

By Ags
in Imaging - Discussion

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Ags

Ags

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What sort of targets are suitable for a 100mm camera lens? you can get good 100mm lenses but i have never seen images taken at this focal length? At F2.0 or F2.8, it should be good for narrowband images...

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Luke

Luke

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If I had a 100mm-ish lens I'd be itching to try:

IC1805 and IC1848 - The Heart and Soul Nebulae

IC 405, 410 & 417 - Flaming Star Nebula, Tadpole Nebula & Spider Nebula

Hopefully they wouldn't be too small in the 100mm and should be good for narrowband.

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davew

davew

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Rosette and Cone. Veil with air around it. North American and Pelican. Butterfly and ( Small ) Crescent. M42 to HH and Flame. Want more ? :)

If you haven't got a 100mm lens yet, I can recommend the Sigma 105mm f2.8 Macro ( It's best at infinity ! )

I use Astrodon 5nm filters. They're ok at f2.8. Wider filters by Astronomic and Baader should be ok too.

If you are very rich and fancy an f2 then I don't know what the filters will do. I suspect you'll get odd results at that angle of view.

Dave.

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Ags

Ags

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The canon F2 is 430 euros, a bit less than the non-L F2.8 macro and apparently a bit sharper. Even that is at the limit of my budget, but it will be worth saving for.

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davew

davew

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I believe that the problems with narrowband at fast FRs is that the pass band moves. I'd have to look it up but if I remember correctly Don Goldman says at f2.8 the 5nm is better than the 3nm but even the 3nm is usable. I can't see any problem at f2.8 and 8nm

When the pass band moves the filter is less efficient at the required line. This becomes noticeable ( I'm told ) at wide angles rather like a Polariser filter. I've not noticed a problem with 5nm at 105mm f2.8. I've not used one at f2 so can't comment on that.

Dave.

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Catanonia

Catanonia

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I believe that the problems with narrowband at fast FRs is that the pass band moves. I'd have to look it up but if I remember correctly Don Goldman says at f2.8 the 5nm is better than the 3nm but even the 3nm is usable. I can't see any problem at f2.8 and 8nm

When the pass band moves the filter is less efficient at the required line. This becomes noticeable ( I'm told ) at wide angles rather like a Polariser filter. I've not noticed a problem with 5nm at 105mm f2.8. I've not used one at f2 so can't comment on that.

Dave.

mmm, I haven't yet tested my 8nm at 568mm Focal length F 2.8 on a 8inch newtonian.

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davew

davew

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F2 is very enticing. I tried an f2 lens once. The edges were so poor it had to be closed down to f4 before it looked almost passable !

That lens I mentioned above is one generation back. It has an aperture ring. The latest one is " Updated ". This can mean worse as well as better. I would recommend buying secondhand. Make sure the vendor will take the lens back if it's not up to scratch. I went to a camera shop and although I explained our position re cloud, they would not budge on returns. Another shop I tried gave me 30 days to test. Guess where I shop ? This applies to any make but I don't know where you'll stand buying new.

There is one poster on here who had a bad experience with a Sigma lens and now won't use them. Discount nothing until you've tried it.

Just to give you an idea of the view, I've included a Rosette and Cone framing test shot. It's just 3 subs of 10 minutes at f2.8 in Ha so not a work of art. My final image was pushed to the right and cropped so won't show the view correctly.

Dave.

post-13139-133877712699_thumb.jpg

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Ags

Ags

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Dave, which lens was that? I'm thinking of the canon ef 100 F2. It has rave reviews on sites like ken rockwell.

Regarding filters and fast optics, I found this note on the TS web site:

Important information for owners of telescopes or tele objectives faster than f/4:

Astronomik filter work very homogen and are nearly free of reflections. But combined with fast optical systems, they change their characteristics and the transmission curves are not optimal any more. This results in abbreviations in transmission from the centre to the edge of field. This happens e.g. with fast tele objectives, Celestron Hyper Star, ASA optics...

If you want to have an optimized filter for such a system, please give us the f/ number and we can deliver by special order an optimized filter for your system. This additional service is free of charge.

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Ags

Ags

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One strange thing about this forum is that you sometimes cannot edit your posts, sometimes you can.

I was setting aside some money to buy a larger scope, but I think this is a winning combination: a macro lens that doubles as a superfast astrograph. It will also do well as a medium telephoto.

We had a photo competition at work over christmas, and my pic made it to the shortlist of 20 out of over 300 - first prize will be a voucher about the price of the canon macro... Fingers crossed!

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davew

davew

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Here's the re framed and cropped image. As you can see I was chasing Ha :)

This is the Sigma 105 f2.8 Macro but NOT the latest version.

That's an interesting piece by Astronomic. I assume ( Could be wrong so don't quote me ) that they'll send you a filter that is slightly off curve the other way. Then if you shoot faster the curve will come back !! Well, I know what I mean.

Two things I'll say here.

1- Make quite sure you can take any lens back after testing if it proves to be less than perfect for your needs.

2- Be sure you'll use the lens more than once or twice. You really have to want this field of view. Other wise buy that scope.

Have fun,

Dave.

post-13139-133877713036_thumb.jpg

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