Hi. Has anyone else had trouble getting focus with this combination? I have my 2600mm bolted to my 36mm EFW bolted to my OAG-L, and the 290mm mini (with extender removed) just barely reaches focus all the way inserted. Indeed, I'm not sure if better focus could beoptained by moving further in (if that were possible). Is this expected?
Marc
marcblank I'm not sure if better focus could be optained by moving further in
Yes. The optical distance from the guide camera sensor (through the prism) to your objective lens will be slightly shorter as you bring the prism closer to the optical axis. (Consequence of the Pythagoras Theorem.)
There is a fine line here. Moving the prism closer to the optical axis will eventually produce vignetting. You want to move the prism as close as possible to the optical axis, as it will produce less star aberrations, too, when sampling a beam close to the optical axis (better star shapes for guiding), but not too close as to produce vignetting.
You can minimize vignetting by rotating the OAG so that the prism is on the long axis of your sensor frame.
Check the documents for your OAG. All OAGs come with screws and such to loosen the prism stem to allow you to push and pull the prism closer and further from the optical axis.
Chen
Hi Chen
Do you have any experience/views on Active Optics Guiding ??
Like this product; Starlight Xpress Active Optics Guiding System USB https://optcorp.com/products/starlight-xpress-active-optics-with-usb-qsi-compatable
Should this maybe become an interesting product for ZWO ??
PS; I got here by trying to figure out the JWST behind the mirror optics and sensors; maybe I should get one of these? https://jwst.nasa.gov/content/about/innovations/infrared.html
galactique Should this maybe become an interesting product for ZWO ??
Why not just buy the Starlight or SBIG (now part of Diffraction, Ltd.) one? Remember that the AO glass is in the light path -- you wouldn't use a cheap filter on a Canon L lens, would you? Can you imagine an AO that produces halos?!
INDIGO (thus INDIGO Sky) has support for at least the SBIG one.
FWIW, I still have a Starlight Xpress SXV9 camera, and an SBIG ST-8300, and both companies produce quality devices.
I have not delve into AO yet; my imaging train is already at the weight limit a small 70+ year old man can carry! But I will probably break down and get one eventually. The main problem may be to accommodate it with the short back focus (56.2mm) of my favorite OTA.
Chen
you wouldn't use a cheap filter on a Canon L lens, would you?
No not me but then in general I only use Nikon, with Sigma prime lenses :-)
You are not alone in the Venn diagram of age > 70 with rig > now too heavy
Cheers
galactique Sigma prime lenses :-)
Can't beat them, IMHO. I have a Sigma 135mm/1.8 ART lens, for the times I need really wide FOV. It is not especially light, though, but lighter than an Askar ACL200, which I use for "somewhat wide" FOV.
You are not alone in the Venn diagram of age > 70 with rig > now too heavy
:-)
Chen
I had this issue, then realized that the camera came with some spacers screwed in by default. Removing some of these spacers took the camera much deeper in, gave me great focus, and lowered the profile of the device!
