FoxK
Carpal Tunnel
Reged: 11/07/07
Posts: 2765
Loc: Cape Cod, MA
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Heya all.
Quick question....I know its recommended that the LS60TCaK/B600/C be used on scopes with a F/L of less that 700mm (iirc) but I was wondering if for NON VISUAL WORK, could one put the diagonal on a larger F/L scope if used for imagery?
I was thinking if it was possible to use my BF600 and use it with my 8" Newtonian with a F/L of 1200mm FOR IMAGERY only. I'm not sure what exceeding the F/L recommended for the BF means...I'm sure for safety's sake one can't apply it to any old scope one has...careful checking must be done to ensure the BF can safely be used, but i was wondering if for imagery, using that BF on a scope exceeding the F/L limit would damage the imager?
All comments welcome
(repeated for safety sake)-never use a BF outside its limitations for visual use!
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Orion 80mm ED Apo Refractor
8" Classic Dob (used as Newtonian on CG5 mount)
Meade 70-AZ-A 70mm Guider using PHD
LS60TCaK/B600/C
CG-5 Advanced GT Mount
Nikon D40x with T-Adaptors
Philips SPC900NC(1/4"ccd)& Quickcam 9000(1/3"CMOS)
Imaging Source DMK 21AU04.AS
- click for cloud prediction for Plymouth, MA. area
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brianb11213
Post Laureate
Reged: 02/25/09
Posts: 3304
Loc: 55.215N 6.554W
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Exceed the aperture limit & the filter may crack or distort. If using with an 8" scope I'd suggest stopping down to 4" to remove the danger.
Exceeding the focal length is less serious, you just won't be able to get the whole disk in the field. If you want to image the whole disk at one go (without mosaicing) with 1200mm focal length, you need the B1200 or B1800 filter.
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bob71741
super member
Reged: 02/16/08
Posts: 123
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I remember that the safety issue with the CaK blocking filter is with the scope's aperture not F/L; any scope over 100mm in aperture will need a ERF to keep the heat down.
Increasing the F/L wrt blocking filter will yield a larger sun than the filter can accommodate.
Bob
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Keith Howlett
Pooh-Bah
Reged: 03/06/07
Posts: 1029
Loc: Northumberland, UK
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Stopped down to 4 inches it will be fine, I think the concern is cooking the CaK module at larger apertures.
I have a variation on the same question...
I have a Lunt CaK module that I'm using with a 4 inch APO. Sometimes I'd like a little more image scale and I'm wondering if I can insert a Powermate ahead of the CaK module without cooking it. Any thoughts?
Thanks,
Keith
Edited by Keith Howlett (11/06/09 09:37 AM)
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FoxK
Carpal Tunnel
Reged: 11/07/07
Posts: 2765
Loc: Cape Cod, MA
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K...sounds like a no-go then. Don't wanna damage the bf600.
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Orion 80mm ED Apo Refractor
8" Classic Dob (used as Newtonian on CG5 mount)
Meade 70-AZ-A 70mm Guider using PHD
LS60TCaK/B600/C
CG-5 Advanced GT Mount
Nikon D40x with T-Adaptors
Philips SPC900NC(1/4"ccd)& Quickcam 9000(1/3"CMOS)
Imaging Source DMK 21AU04.AS
- click for cloud prediction for Plymouth, MA. area
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colinsk
Carpal Tunnel
Reged: 01/17/08
Posts: 2170
Loc: CA
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There are two issues here. Larger aperture gatherers more heat and the system was only recommended to 100mm do to heat rejection. The second issue is image size. If you have a very long lf telescope the image size of the sun will exceed the diameter of the blocking filter. This will no damage the BF600 but will limit the field of view. If you take the fl/100 you have a pretty good guess of the solar image size. Losing say half of this image by using a Powermate would lower the energy on the BF600 not increase because much of the solar disk would end up outside of the filter and get absorbed in the housing.
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Mahalo,
Colin Kaminski
Coulter 10.1" Dobsonian
TV-76/Baader Film White Light
LS60T/DS50/FT/BF1200
LDX-75
AT Voyager
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brianb11213
Post Laureate
Reged: 02/25/09
Posts: 3304
Loc: 55.215N 6.554W
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Quote:
Sometimes I'd like a little more image scale and I'm wondering if I can insert a Powermate ahead of the CaK module without cooking it.
There's no safety issue here but there may well be a practical one. The Lunt CaK module has a L-O-N-G barrel which inserts into the focuser, you may not be able to get it inserted far enough into the Powermate to be able to achieve focus.
In any case, using a "shorty" barlow after the CaK module is effective; and a Barlow used with a monochromatic filter (be it CaK or Ha) does not have to be well corrected for false colour, so a cheap one will probably be fine.
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Keith Howlett
Pooh-Bah
Reged: 03/06/07
Posts: 1029
Loc: Northumberland, UK
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Hi Colin & Brian,
Thanks for the comments. I was a bit concerned at cooking the Powermate but that would be easy enough to check.
You have a good point about the CaK module's length, about half of the CaK module barrel actually fits into the Powermate, the scope has a good amount of back-focus but it's not obvious that it will reach focus. It looks like I'll need to try it. Thanks also for the tip about the shorty barlow.
Cheers,
Keith
Edited by Keith Howlett (11/06/09 12:19 PM)
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Fish
sage
Reged: 10/13/07
Posts: 475
Loc: Norridgewock, ME
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Good evening,
As seen in the description below, I use a Lunt CaK module with a 102mm aperture. Although strictly speaking the module's specs say 100mm is the limit I felt the 4% increase was within the filter's safety limits. Disclaimer: I do not view visually through this system.
As for the blocking filter only the FOV will be affected. This can be used to advantage within the host telescope's limits; closeups of surface or edge feaures are easier to image with less hassle.
Regards, Marc
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Goseck Observatory
Kunming 152 f/5.9 & Baader Wedge
Orion ED80 & LS75FHa2/B1200
Meade 102ED & LS18CaKMDd2
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Keith Howlett
Pooh-Bah
Reged: 03/06/07
Posts: 1029
Loc: Northumberland, UK
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That's the idea. IIRC Markus did say that the 100mm limit did include a substantial safety margin.
Cheers,
Keith
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