Fine tuning rings??

[banner001]

Ok i get the idea that they decrease focal length, so a 10mm EP becomes a 6mm (effective) etc... but what effect does this have on the image?

Ok hypothetical question...i buy a 10mm EP and its corresponding 20mm fine tuning ring...what will this make the effective EP focal length? can someone point us to a calculation...

also what does this do to coma (i have a fast reflector), chromatic arberation, contrast etc...

and finally if the 10mm EP + ftr = 7mm...would a 7mm from the same company be "better" than the 10+ftr?

please ignore cost, i know that a ftr at £10 is cheaper than several EP's at £100's each...putting that aside is there any difference?

cheers!

[banner001]

shameless bump for help?

[jgs001]

I've a set of fine tuning rings for my Baader Hyperions. The lower cell of the eyepiece is, in fact, a barlow, so putting the FTR's in, moves the barlow further away from the ep, giving you a boost in the magnification, or an effective reduction in the focal length of the ep. I've only ever used them in refractors, including an f/5 ST80, and not noticed any issues in doing so. Not sure that answers all your questions, but HTH

[banner001]

I've a set of fine tuning rings for my Baader Hyperions. The lower cell of the eyepiece is, in fact, a barlow, so putting the FTR's in, moves the barlow further away from the ep, giving you a boost in the magnification, or an effective reduction in the focal length of the ep. I've only ever used them in refractors, including an f/5 ST80, and not noticed any issues in doing so. Not sure that answers all your questions, but HTH

ive bought a hyperion 8mm (150x mag), was thinking of getting the 14mm and 28mm ftr to convert it to a 6/5mm focal length (200x or 240x mag), if there is no difference between using the ftr and buying the proper EP, its definitely worth a look at...

[jgs001]

They are cheap enough, that it's worth a try anyway.. much cheaper than more Hyperions...

I've never had the matching fl ep, to the ones I've got with the FTR to directly compare... but given the FTR's don't add glass to the mix they won't directly reduce the quality of the view.

[Ags]

Just be aware that you might not be able to bring the EP to focus with the fine tuning rings in place. I tried my 17mm with ftr in a cheap reflector and could not achieve focus.

[Ags]

I have the feeling that ftrs are more often bought than used. I've never used mine after the first unboxing.

They might be useful if I upgraded to an 18mm speer-waler. I could just recycle my 17mm hyperion as a 13mm.

[Damo636]

I have both fine tuning rings and use them regularly with the 8mm. I find they work really well. They give me an additional 6mm, 5mm and 4.3mm f/ls. For about £16 its a no brainer! As stated above the ring does not degrade the quality of the image as you will not be adding any more glass, just moving the Barlow element further away and so by increasing the magnification.

[Ags]

Glad you like them damo. I've reread my posts and they seem a bit negative. I will have another go with my ftr on a suitable target like M13.

[Moonshane]

I have only ever used then for screwing on the end of my 13mm Ethos to make it 2" only and for extending my 2"-1.25" adapter to prevent me breaking 2" filters with my longer 1.25" eyepieces (the Nagler zoom pokes through by a quarter of an inch without it).

[Ags]

I tried out my 14mm fine tuning ring on some globular clusters tonight. The hyperion yielded 100x with the FTR in place. M3 was partially resolved and M13 was quite well resolved with this combination, while the magnification of 100 still allowed the 'fuzz' of the globulars to be seen, so the view was preferrable to higher powers like 150x which didn't seem to resolve any more stars tonight (it was quite a dark night anyway).

The combination also split the double double, so the EP works very well with the FTR in place. I take back all my grumbles about FTRs! My 17mm is now officially a 13mm!