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Old 01-06-2012, 08:06 AM
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cometcatcher (Kevin)
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Reviving old non-APO refractors with filters?

Hi guys, I'm an old school, film era deep sky astro-photographer getting back into astrophotography now with my very first ever DSLR camera. I still have the old achromatic refractors. With film, purple fringe and bloating wasn't a problem, but of course now with digital my old lenses all look like they are made with 1 dollar plastic lenses lol.

The way I see it I have two choices. One is to try and revive them with some kind of fringe or UV/IR cut filter in the path, or two to bite the bullet, forget the old gear and save for a new APO imaging refractor. This may take a while as my $ to spend on astro gear is limited.

In order to help me decide I've been trying without success to find before and after shots with various UV cut filters on basic refractors. I'm sure there must be a myriad of threads here on the forum, but I suck at finding anything.

If anyone has some before/after image examples or advice I'd be very grateful.

P.S. This is for 600mm f/L and shorter as when I reach 750mm it's reflectors from there on.
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Old 03-06-2012, 01:53 AM
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pmrid (Peter)
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Quote:
Originally Posted by cometcatcher View Post
Hi guys, I'm an old school, film era deep sky astro-photographer getting back into astrophotography now with my very first ever DSLR camera. I still have the old achromatic refractors. With film, purple fringe and bloating wasn't a problem, but of course now with digital my old lenses all look like they are made with 1 dollar plastic lenses lol.

The way I see it I have two choices. One is to try and revive them with some kind of fringe or UV/IR cut filter in the path, or two to bite the bullet, forget the old gear and save for a new APO imaging refractor. This may take a while as my $ to spend on astro gear is limited.

In order to help me decide I've been trying without success to find before and after shots with various UV cut filters on basic refractors. I'm sure there must be a myriad of threads here on the forum, but I suck at finding anything.

If anyone has some before/after image examples or advice I'd be very grateful.

P.S. This is for 600mm f/L and shorter as when I reach 750mm it's reflectors from there on.
Kevin, I have tried Baader Fringe-Buster filters with an old achromat in the hope of eliminating the bloating of stars in the images. Unfortunately, it didn't really make a sufficient difference to encourage me to press on with that plan. Also, it gave a jaundiced yellow tinge to everything. I was using a one-shot colour camera at that time.
I figured that the only way I could make use of the achromat was with narrowband filters and a mono CCD where you can focus each filter individually. That would work OK.
Peter
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Old 03-06-2012, 02:36 PM
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Thanks Peter, that's the info I was looking for. I will only be shooting single shot colour so it looks like I will be saving for an APO refractor.
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Old 04-06-2012, 08:59 AM
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PRejto (Peter)
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Maybe slightly off topic, but I did try out my 5" f15 achromat on Saturn back in April. I wanted to compare it to my TEC140, which obviously won, but not by all that much. I used a one shot colour camera (DBK21AU618) so this would not be ideal....no filters other than UV/IR.
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Old 04-06-2012, 06:38 PM
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Hi another Peter. They're still good images. Running at F15 would help also. My problem is I want to run one at around F5.

Actually my photography isn't that good anyway and there are worse things for me to worry about than colour flare atm.
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Old 04-06-2012, 08:35 PM
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dannat (Daniel)
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It's not that hard to find photoshop or other processing plug in to remove the violet halo from your old film lenses, if you stop them down 1-2 stops you can get away with it, just a small violet removal & it will look fine
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Old 05-06-2012, 03:03 PM
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cometcatcher (Kevin)
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Yeah it didn't help that I was running some of my tele lenses at full aperture for deep sky. I will stop down a bit next time.
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