Quote:
Originally Posted by thefrogulox
Troy,
I have a TMB92ss and have been using the Astro-Tech field flattener recommended by Astronomics. I have found that it does the job nicely.
Due to the recent inclusion of an OAG in my imaging train, the Astro-Tech is no longer suitable as the OAG adds too much back focus for it.
Annoyingly, I can't put the OAG before the flattener (relative to the focuser) because the flattener's nosepiece is not removerable!
I am therefore considering purchasing the WO FF4 as it allows for considerably longer backfocus.
How have you experiences been with the TMB and WO FF4? Does the flattener perform well with the scope?
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G'day mate. Funnily enough, I was going to test the WO4 just the other night, but guide camera failed on me so didn't get it done. I will some time this week I reckon. Certainly doesn't achieve focus with that OTA extension on it, so have to remove it. ie have FeatherTouch connected direct to white OTA, not the black extension.
By the way, I've ordered the Televue TRF-2008, and if it delivers what I'm after, I'll be selling the WO4
Quote:
Originally Posted by bmitchell82
Something that everybody has failed to mention is glass.....
I have a mixture now of 4mm FLI LRGB filters and Astronomik NB filters (I think 2mm?) the focus shift is quite substantial!
I will have to find the formula for it but in my system according to my FT scale its put nearly 5mm extra back focus required.
I know its not 10mm but if you added all your mechanical tolorances together your within the flatteners tolerances and hence your stars are happy again.
Thats my experience with Filters, Mono cameras and Flatteners/Reducers
BM.
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Pretty sure the Astronomik filters are 1mm thick. And I think the rule is that they add 1/3 of their thickness to the light path, ie increase focus distance by that. My Astrodon LRGB filters are 2mm thick IIRC and as you mention, there's noticeable focus distance between them. Haven't measured if it's the 0.33mm difference based on above calcs. Would be an interesting exercise to see if it is around that.