Vixen ED81S Back Focus/Tubes

[hatflyer]

I have the ED81S. I am trying to find out what the back focus point should be when using the Vixen flattener/reducer. Not getting answers from various shops. Anyway to find out?

Also, I have this sequence of components - camera, T2 ring, T2 to 60mm adapter, the flattener/reducer (60mm thread on both ends), then to the focuser (60mm). I'd like to get a set of tubes so I can get what distance I need, including when I don't use the flattener/reducer. But having trouble finding such a set. Most are m42 or M48.

Any ideas on what to do?

Thanks.

PS. Since the scope has several inches of focus adjustment, why do I have to find extension tubes to get within 1mm of the proper back focus? A quick look allowed me to get an image in focus with the focuser, even tho I don't know the back focus plane.

[chartram]

M42 is the same as T2. This threw me when I first started too. Plenty of spacer tube sets on the market to get you within +/- 1mm of proper backfocus. I assume the backfocus you need is the ‘usual’ 55mm(?) That’s pretty standard among flattener/reducers for refractors.

The flattener/reducer’s function is to correct the image hitting the camera sensor. In order to do that effectively, the flattener/reducer needs to be a specific, standard distance from the sensor. The flattener’s distance requirement being relative to the camera sensor (not the telescope’s objective lenses) is why it doesn’t matter how many inches of focuser travel you have. Hope this helps.

Mike

[JayTee]

Hi HF,

Your questions about your specific setup are essentially asking for a "turn-key" solution that the vast majority of the AP crowd had to figure out on their own (myself included).

Your question about your specific setup and gear makes it problematic for someone to answer. They actually need to possess the gear in question and they have to be aware of your AP goal.

The vast majority of the AP crowd buy their primary gear and then figure out on their own just what extra accessories they need because there is no "standard" setup. Specifically, as it relates to FFs, FRs, spacers, and extension tubes.

I know this doesn't help initially, but in the long run, you will have a better understanding of what your setup needs to function the way YOU want it to.

Cheers,

[chartram]

So I found this link, there is a Q&A section at the bottom of the page. One of the staff cited the backfocus distance as 63.5mm.

https://www.bhphotovideo.com/c/product/ ... r_for.html

I searched the ED81S (nice scope!), the site mentions another attachment for using the included reducer that is sold separately.

Like JT said above, this hobby is difficult in that we’ve all pieced our setups together, through trial and error and with a vast range of gear. What kind of camera do you intend to use?

Mike

[hatflyer]

So I found this link, there is a Q&A section at the bottom of the page. One of the staff cited the backfocus distance as 63.5mm.

https://www.bhphotovideo.com/c/product/ ... r_for.html

I searched the ED81S (nice scope!), the site mentions another attachment for using the included reducer that is sold separately.

Like JT said above, this hobby is difficult in that we’ve all pieced our setups together, through trial and error and with a vast range of gear. What kind of camera do you intend to use?

Mike

Thanks. I finally heard back from the seller, giving the same distance.

Looks like I am probably all set. My Nikon D5500, then a T-ring, then a wide angle adapter, then for the reducer/flattener combo; or if just a flattener, the same without the wide angle adapter. No extension tubes needed.

Can't seem to find the Vixen flattener itself (u have to buy a whole kit), so will likely use another brand's flattener.

Thanks.