Revelation Astro Eyepieces

[dcwales2012]

HI,

I have asked this question before in the eyepiece section, but replies were few and far between, however I appreciate the reply I received. The reason I'm asking again here is because I might get a wider audience and I want to contact the supplier sooner rather than later if there is a problem.

My family bought three Revelation Astro Plossl Eyepieces for me; 9mm, 15mm and 32mm. Saturday night was the first time I had the opportunity to try them out in anger.

I currently use a Tal 2x Barlow and I was concerned when I noticed the 9mm and 15mm EPs do not sit flush in the Barlow top, part of the silver barrel was visiable. They sit about 4.5mm proud of the top of the Barlow. The 32mm EP sits nicely in the Barlow, having a different type of barrel to the other two. Picture below hopefully shows the issue!

Does it matter the barrel of the eyepieces are too long for the Barlow and protrude?

Will it affect performance, other than changing the focal achievement point?

A bigger concern is the Barlow locking screw isn't sitting in the barrel groove, it locks directly onto the flat; (can't think of a word to describe this, knowing the barrels round not flat), part of the barrel about 4.5mm below the groove, pusing the EP over slightly. Does this matter?

If its not a fault with the eyepieces just the difference in TAL Barlow receptacal depth to Revelvation barrel length, can one buy 1.25" shorter barrels separately, if so anyone have any ideas where from?

Last question, why do EPs coming with different lengths of barrels, for example a Skywatcher Super Plossl 7.5mm has a 22mm barrel, and the Revelation Astrol 9mm & 15mm EPs have a 30mm barrel length?

I help would be very much apprecaited.

Cheers, David

[Capricorn]

It is basically irrelevant.

The chromed tube you have is just longer then the recess in the barlow and the chromed tube may be correct, the design could be that an image plane of the eyepiece is xmm above the tube end so the tube is therefore the length it is to accomplish this.

Most probably it's not that at all but it is one possible reason.

A simpler one is that all the plossls have one tube attached of one length and that is it, economy of making just one chromed tube.

I would actually suspect that plossl's up to 10mm have a short tube, 11m to 20mm have a medium tube and above 20mm have a long tube. They come out looking different and just 3 tubes are made.

Concerning the screw not being in the recess again just the way it is. there is not a universally recognised design for these. The recess is there I suspect becasue others have them and it looks good. If they are meant to be there then Meade will make their holders to use their eyepieces with their barrel on, Celestron will do their own as will Pantax, TV, ES and all the othrs. So back to a mixture, exactly as we have now.

Plossls are not high precision items that are produced to an accurate and repeatable engineering standard. They are turned out by the million by several manufacturers. I gave 3 away some weeks back that is basically the "expense" of the things.

No way will the manufacturers sit down and come to an agreed standard for the chrome barrels on eyepieces, that implies making the eyepiece attachment to the corresponding standard also, it simply is not going to happen - whose present standard gets accepted and do the others therefore start to change their manufacturing equipment to make a different design at some cosr?

Simple answer No, not a chance.

So no, the tube length and therefore how much protrudes is just the way it is, and the recess for the screw is most likely just to make it look "good" and to be like all the rest.

Never seen anyone advertising alternative barrels, could try Astro Engineering but I doubt they will have made any, they are however the only ones I can think of. The cost of production is possibly too high for waht they could sell them for. Get some used cheap plossl's and use the chrome tube from these is probably the cheapest and only option.

[dcwales2012]

Okay. Many thanks for the reply.

Regards

David

[dcwales2012]

I have found a solution to my problem, which has set all my EPs at the same focal depth in the TAL Barlow:

http://www.harrisontelescopes.co.uk/acatalog/Revelation_1.25__Parfocalising_Rings.html

[E621Keith]

Like Capricon said, it doesn't really matter. The astronomical standard 1.25" and 2" fitting aren't standard at all. There's nothing saying how long the barrel protrude, dimension tolerance, or where to put the safety grove. There isn't even anything saying the barrel diameter. It's just ever one seems to be using the 1.25" and 2" fittings so everyone else make parts for these dimensions. Some eyepieces fits tighter, some looser, some has safety grove, others don't, and some uses a taper recess.

This lack of 'standard' allow mix and match of parts from various manufacturer who may have never talked to each other, but sometimes it results in minor incompatibly. For example, some barlows protrude so far inside the tube that there is a real risk of hitting the diagonal mirror, and sometimes screw in filters won't screw in because of a slight dimension mismatch.

If you look at optics market govern by manufacturer standards, you will found a total lack of cross manufacturer compatibility. Spotting scope eyepieces and camera lens from one manufacturer will not fit scopes or camera from other manufacturers. In the case of Nikon, there are 3 incompatible spotting scope eyepieces fittings for different series.

The current astronomical 'standards' I'm aware of are

1. 1.25", 2" eyepiece fitting

2. Tamron T mount for camera connection (because the T-mount was designed for Tamron lens to fit various SLR manufacturer's body)

3. Vixen and Losmandy dovetails (because of popularity of Vixen and Vixen clones, and Losmandy among premium mount users)

4. ST4 auto guider standard. (SBIG invented the ST4 and it became so popular that it's protocol was adopted by others)

5. ASCOM - The only real standard in amateur astronomy that deals with communications and control for various components.

So don't worry about your eyepiece doesn't fit all the way in. There's nothing wrong with either eyepiece or barlow

[John]

One reason for the barrels of eyepieces to vary in length is that many designs require optical elements to be installed there as part of the optical design. With those, if you remove the barrel, the eyepiece won't work.

I guess it's our fault for wanting generous eye relief and wide, well corrected fields of view

[dcwales2012]

Thank you for the replies. Guess all is as it appears.