Jump to content

When imaging is my FL different than observing?

swag72

By swag72
in Imaging - Discussion

Recommended Posts

swag72

swag72

Posted
Posted

I have got a 0.85x focal reducer that I have to use when I attach the DSLR to my Skywatcher 120ED scope. I was told I would need this to get the camera to focus correctly.

Does this mean that when observing using the EP the scope is a 900mm FL and when imaging and the fcocal reducer is attached my equivalent FL is 765mm?

Link to comment
Share on other sites
Psychobilly

Psychobilly

Posted
Posted

yes...

Dont see what the FR as far as helps with focusing is concerned... you could get the scope to focus without it but would normally need to add around 50mm of extension tube as your using the scope straight through rather than with a diagonal...so you need to compensate for the shorteneign of the optical path.

The FR will (or at least should) reduce the FL, increase the FOV and give you a smaller focal ratio for faster imaging and flatten the field (which is what they are often used for)... you can also get flatteners that are not reducers...

Billy...

Link to comment
Share on other sites
swag72

swag72

Posted
  • Author
Posted

Ahh, I see, so if I got a piece of extension tubes I'd have a 900mm scope, with the FL reducer a 765mm scope and then endless possibilities with the DSLR and lens's.

Cheers for that - May have to get some extension tubes stuff then - FLO the place to shop? I hope it's not that nuts and bolts shop again!!!!

Link to comment
Share on other sites
Psychobilly

Psychobilly

Posted
Posted

Yeah FLO are some of the Decent Guys and forum sponsors and with some items you may still get forum discount...

Based on Martins last post try it... looks like there may be enough outward travel on the focuser without needing an extension... I have always used shorter FL fracs and they have always needed an extension...

Billy...

Link to comment
Share on other sites
Psychobilly

Psychobilly

Posted
Posted

Indeed...

and all the grief that the longer focal length and slower focal ratio will bring... for web use your can often be better off taking a 100% pixel crop from an shorter and faster setup...

Once you start guiding you will get more repeatable results at longer FL and slower FR ...

But go for it :eek:

Billy...

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.