caober Posted July 14, 2020 Report Share Posted July 14, 2020 (edited) Hello all. I have a new to me 10N and 3" Televue Paracorr 2 that I'm having trouble getting anything near round for the stars. Even when centered, stars are triangular or 3 lobed shapes. My image train is the OK3Z focuser, extension plus holder, Paracorr with AVI-3200 imaging system adapter, imaging system-M42 adapter. The camera for the tests is an SBIG STF-8300 with the FW8 filter wheel and OAG. Backfocus of the combination is 57.5mm. My collimation is close but not spot on yet. Is my problem the spacing, image-train, collimation or something else? I have a Takahashi Epsilon too but have never experienced star shapes like this throughout the field. The test images attaches were 60" unguided on a Paramount MX. Full resolution and fits are available here: https://www.dropbox.com/sh/ikcd367mt79mb62/AACZkqmjRXcEf_TF803UnIJUa?dl=0 Thanks for any assistance you can lend. Chris Edited July 14, 2020 by caober Link to comment Share on other sites More sharing options...
MarkS Posted July 16, 2020 Report Share Posted July 16, 2020 Chris, Don't worry about collimation for the moment. The three images you present do not all show the same characteristics: I guess that the focus settings were not the same for each shot. However, the aberrations are roughly symmetric in each, and the CCDI image of curvature is symmetric. But the curvature is awful! I am not familiar with the Parracor, but I suspect that the backfocus distance of 57.3mm, which is correct for the ASA 3" Wynne (measured from the front face of the Wynne to the image plane) is not correct for the Parracor. I don't know what information is available for the Parracor, but I suggest you start there, unless you can get a ASA Corrector.... Perhaps others may be able help more than I? Regards, Mark Link to comment Share on other sites More sharing options...
caober Posted July 16, 2020 Author Report Share Posted July 16, 2020 Thanks Mark. Paracorr 2 backfocus is reported to be 80mm. The mechanical drawing shows 73.3mm from the end of the tube. http://www.televue.com/engine/TV3b_page.asp?id=61&Tab=_phot3 Link to comment Share on other sites More sharing options...
MarkS Posted July 16, 2020 Report Share Posted July 16, 2020 So you need a 14mm spacer to increase the backfocus distance. Then there is the matter of the axial position of the Parracor in the focuser to ensure you can reach focus. The ASA Wynne barrel design ensures this happens - you may need to experiment to find to right position for the Parracor. Mark Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now