Concerned about Barlow

[Astrosurf]

I've got this 2X Barlow but it wouldn't fit to my SW 200P.

First Light Optics - Skywatcher ED Deluxe 2x two-inch Barlow Lens

I'm asking FLO about it but they're not too sure if I will achieve focus with my Canon. I also need this adaptor as well.

First Light Optics - FLO 2-inch T mount camera adapter

This will extend the length. Does anyone know if this set-up will work with my DSLR?

Alexxx

[barkis]

I've got this 2X Barlow but it wouldn't fit to my SW 200P.

First Light Optics - Skywatcher ED Deluxe 2x two-inch Barlow Lens

I'm asking FLO about it but they're not too sure if I will achieve focus with my Canon. I also need this adaptor as well.

First Light Optics - FLO 2-inch T mount camera adapter

This will extend the length. Does anyone know if this set-up will work with my DSLR?

Alexxx

What do you intend imaging with the Barlow in place Alex,

I am assuming the Moon/Planets ?

Ron.

[steppenwolf]

I have tried one of these on a refractor for imaging and it added significantly to the backfocus so I suspect this will be an issue with your Newtonian reflector when used with a DSLR camera.

[Astrosurf]

I hope to increase mag on small DSOs.

What exactly do you mean by backfocus? Is that just achieving focus? Sorry to be thick!

If this is going to be an issue I'll have to ask for a refund, or try to sell it on. I haven't much money left so an extra £20 for a extra piece that might not work is a bit of a worry.

[steppenwolf]

The easiest way to be sure is to attach the Barlow to the focus tube and during the day, point the telescope at a distant object (electricity pylon, church spire, block of flats for example but be sure to avoid the Sun) and then hold the camera over the end of the Barlow and move the focus in and out whilst looking through the viewfinder. See if you can achieve focus. If you can't get close enough IN then you don't have enough 'backfocus', and it will never work with your telescope. If you feel that you need to move the focus further OUT than it will go then you could use extension tubes in front of the Barlow lens to achieve focus.

[steppenwolf]

This thread may have some relevance to your query, Alex.

[Astrosurf]

Many thanks Steve. I'll give this a go.

[russ.will]

Not that I wish to contradict Steve (Great book, by the way ), it's use of the SW extension tubes that cause the problems with the stock SW focuser. As they have to fit inside the the clamping ring in the top of the draw tube, their internal diametre is considerably less than 2" - Thus, the long ED barlows get stuck way to far out and there's insufficient 'in' focus to compensate.

Take the extension ring off and the barlow will happily fit in the focuser, but you'll need experimentation to find the point where it brings the camera (or EP) to focus. If you're only using the barlow for imaging purposes, this point can be cemented in place with a 2" parfocalizing ring.

Russell

[steppenwolf]

No contradiction there, Russ, the thread I link to discusses this point too. This is one of those occasions when you wish the gear was in front of you because the issue would be quickly apparent I think! Stick it in the post to one of us Alex (but not really ...)

[Astrosurf]

I might hold off sending it back to FLO until SGL7 as I can ask there!