Focal Reducer on ebay

[zakkhogan]

Hi all,

Ive seen thsi on ebay and i wondered if anyone could shed some light on the item

http://www.ebay.co.uk/itm/0-5x-telescope-eyepiece-focal-reducer-/160842043412?pt=UK_Telescope_Eyepieces&hash=item2572eed014

it says is a 0.5x focal reducer. i get the its cheap, and has no corrector,

I have an 8" F10 sct, will this give me an f5?

or am i completely barking up the wrong tree?T

Thanks

Craig

[scarp15]

Hi

I really dont know anything about this one, I have the Celestron F6.3 reducer / corrector, which I use occasionally with my C8 for visual, and find it most useful with my 1.25" eyepieces.

They sometimes come up at a faitr price on astro buy and sell, if you did not wish to purchase at retail.

[Cornelius Varley]

That type of focal reducer changes the focal length of the eyepiece it is attached to. So a 20mm eyepiece would have a focal length of 40mm with the reducer attached.

Peter

[GlassWalker]

I think I have that same one, in my case sold as an Opticstar where they have more info on its use.

The focal reducer does what it says on the tin, providing you put it at the right distance from the focal plane. Reduces the effective focal length of the objective system, and by definition the focal ratio changes too. I haven't come across thinking about its action on the eyepiece, but I am biased towards imaging so most of the time don't use any eyepiece.

[zakkhogan]

i was going to attach it to my dslr,

how will this affect me setup?

[alan potts]

Yes it would but I am not to sure how good it will be for visual work. I have a reducer to F6.3 by Meade, all the top brands have one. I would recomment you save for one of these. Even these are limited as to what you can do with them.

I made the mistake of believeing that I could bang on a 40mm 2inch eyepiece and see behind me, WRONG. With 2 inch diagonals the eyepiece max is 28mm or you will get vignetting at the sides. I do like them as they give a wider FOV in SC scopes, with your scope you should get almost 2 degrees if you go down the 2 inch road. With normal 1 1/4 inch eyepieces I believe you can go to 40mm but I have never needed to try it.

With this o.5 reducer you will get a reduction for sure but you may be limited to even short F/L epepieces. Save for the better quality reducer. You may even get one second hand if you wait.

Alan.

[GlassWalker]

The possible problem with using this reducer on a DSLR is the reduced image circle. For example, when doing a test in daytime before and after fitting the reducer on the Nexstar 4SE:

Note distance might not be correct for exactly 0.5x. I haven't used this configuration for night sky usage since I have other shorter/faster optics anyway, so can't comment on image quality although I didn't see anything objectionable in the above test.

So assuming your scope takes a 2 inch one, you're probably better off looking for one in that size if you need to cover a DSLR sensor. Otherwise this may be more suitable for use with a smaller sensor CCD.

[zakkhogan]

Thanks guys, another very informative read, thanks for all the good advise

[Michael1971]

Hi, Focal reducers mostly work fine with EP but on camera's you have to account for the focus point.

That 0.5 from ebay, I have that one, when screwed on a webcam adapter its impossible to reach focus because the focal point is almost 50% inwards.