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Equipment Discussions >> Binoculars

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PowellAstro
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Reged: 10/14/09

Loc: Tennessee
Re: Findings with Celestron SkyMaster 15x70 binoculars new [Re: PowellAstro]
      #5979861 - 07/19/13 01:59 PM Attachment (58 downloads)

Here is a shot after I blackened the inside of the body and the edges of the prisms. This shows the prism clips.

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PowellAstro
scholastic sledgehammer
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Reged: 10/14/09

Loc: Tennessee
Re: Findings with Celestron SkyMaster 15x70 binoculars new [Re: PowellAstro]
      #5979871 - 07/19/13 02:03 PM Attachment (48 downloads)

And a shot of the now Blackened Barrels:

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PowellAstro
scholastic sledgehammer
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Reged: 10/14/09

Loc: Tennessee
Re: Findings with Celestron SkyMaster 15x70 binoculars new [Re: PowellAstro]
      #5979878 - 07/19/13 02:05 PM Attachment (51 downloads)

This shows bad reflections in the non-blackened lens edges in the stock eyepiece and these major reflections now much cleaner in the eyepiece with the blackened edges:

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PowellAstro
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Reged: 10/14/09

Loc: Tennessee
Re: Findings with Celestron SkyMaster 15x70 binoculars new [Re: PowellAstro]
      #5979890 - 07/19/13 02:09 PM Attachment (47 downloads)

The eyepiece field stops were also found to be a major source of reflected and scattered light. They are made of a very shinny plastic and produce a lot of glare. These were blacked out as well:

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Rich V.
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Reged: 01/02/05

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Re: Findings with Celestron SkyMaster 15x70 binoculars new [Re: PowellAstro]
      #5979939 - 07/19/13 02:36 PM

Hey, Glen, have you determined just where in the system the 70mm objectives are stopped down to the effective 63mm that has been measured in all of this style of binos? I'd expect it's the front prism aperture but can't say for sure.

Since you're being so thorough, I'd like to hear what you have to say about this...

Enjoying your well documented breakdown! You'll have the best pair of Skymasters in the country when you're finished!

Rich


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GlennLeDrew
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Re: Findings with Celestron SkyMaster 15x70 binoculars new [Re: Rich V.]
      #5980021 - 07/19/13 03:29 PM

Rich,
Yes, it's the frontmost prism aperture which stops down the system.

PowellAstro,
Good looking work! Some questions:

- Did you also dull the shiny inside surfaces of the eyepiece spacer rings?

- How did you measure the eyepiece and objective focal lengths?

- You mention your suspicion that the prisms are likely the 'weak link.' Do you have a small optical flat to place against prism surfaces so as to assess the degree of flatness?

- Upon reassembling, how are you ensuring there is no prism 'lean' (which if present would introduce image rotation and eye strain)?


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PowellAstro
scholastic sledgehammer
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Reged: 10/14/09

Loc: Tennessee
Re: Findings with Celestron SkyMaster 15x70 binoculars new [Re: Rich V.]
      #5980026 - 07/19/13 03:32 PM

It is the front prisms that stop them down. Good news, I now have the full 70mm use of the objective lenses! I moved the lenses back in each barrel just over 1/4 inch. The center of the lenses are now flush with the outside edge of the barrels. With this I now have fully illuminated exit pupils all the way around! I can also now focus as close as 32 feet and still have a 1/3 turn left on the focus knob. I have no idea other than their lock ring setup, as to why they had the lenses screwed so far into each barrel. Mine are back together now and they look like a 500 dollars pair of binos. Images are very sharp, contrasty and with way better color saturation!

I will document all that I have done to them as soon as I can pull it all together. I am glad to answer any questions.


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PowellAstro
scholastic sledgehammer
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Reged: 10/14/09

Loc: Tennessee
Re: Findings with Celestron SkyMaster 15x70 binoculars new [Re: GlennLeDrew]
      #5980037 - 07/19/13 03:40 PM

Quote:


- Did you also dull the shiny inside surfaces of the eyepiece spacer rings?





Yes, I did all spacer rings in the eyepieces as they are of the same shinny material.

Quote:


- How did you measure the eyepiece and objective focal lengths?





I use the sun and a slide rule jig made just to test FL.

Quote:


- You mention your suspicion that the prisms are likely the 'weak link.' Do you have a small optical flat to place against prism surfaces so as to assess the degree of flatness?





Yes I do and most are 1/2 wave, some close to 1/4.

Quote:


- Upon reassembling, how are you ensuring there is no prism 'lean' (which if present would introduce image rotation and eye strain)?




I have a bino laser collimator I use.


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Andresin150
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Reged: 08/14/07

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Re: Findings with Celestron SkyMaster 15x70 binoculars new [Re: PowellAstro]
      #5980067 - 07/19/13 04:02 PM

Excellent! for a moment I wanted a Skymaster to experiment too!

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GlennLeDrew
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Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: Findings with Celestron SkyMaster 15x70 binoculars new [Re: Andresin150]
      #5980527 - 07/19/13 09:26 PM

Having moved the objective that 1/4" farther out, this must leave not much extra in-travel beyond infinity focus.

Are you certain you now have full aperture performance? For unmodified binos which have a 22mm aperture prism stopping the system down to 63mm, the on-axis beam footprint at the front prism aperture would be 70 / 63 * 22 = 24.4mm. For an f/4.7 objective, moving it out 6mm increases the light cone diameter at the prism by 4.7 / 6 = 0.78mm, which is rather less than the required 2.4mm.

Are you aware of the flashlight test for effective aperture? This will provide a direct measure. Remember to set the focus for infinity, and to locate the flashlight a good foot or so from the eyepiece.


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PowellAstro
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Reged: 10/14/09

Loc: Tennessee
Re: Findings with Celestron SkyMaster 15x70 binoculars new [Re: GlennLeDrew]
      #5980555 - 07/19/13 09:45 PM

You are correct. If you look in the pic that shows the prism you will see the hole is now open to the very edge of the larger prism. I milled the front holes 3mm larger on the CNC as part of this mod. The large prism were right at 25mm wide. Due to better optical alignment, the edge correction looks better than it did before this work. I was worried the edge correction might look bad but it turnned out to be fine. As to the focus I have about a 1/3 turn left after focus at infinity.

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PowellAstro
scholastic sledgehammer
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Reged: 10/14/09

Loc: Tennessee
Re: Findings with Celestron SkyMaster 15x70 binoculars new [Re: PowellAstro]
      #5980594 - 07/19/13 10:25 PM

About your flashlight test. I have a 20" diffusion panel that I use. Before the mod, you could see vignetting around the exit pupil. Using a fully illuminated light source and focus set at infinity, the exit pupils are now fully illuminated with no detectable vignetting and the exit pupils measure 4.67mm. This is what should be seen with 70mm lenses of 330.2 FL at 15x.

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GlennLeDrew
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Re: Findings with Celestron SkyMaster 15x70 binoculars [Re: PowellAstro]
      #5980821 - 07/20/13 02:33 AM

You say the first prism to intercept the light from the objective is the larger 25mm width, compared to the second, which is 22mm? If so, I'm a little surprised. And furthermore, that the first prism opening was not enlarged so as to take advantage of this and thereby gain back the full aperture is another puzzling aspect.

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nicknacknock
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Re: Findings with Celestron SkyMaster 15x70 binoculars new [Re: GlennLeDrew]
      #5980927 - 07/20/13 06:05 AM

Really enjoying this thread.I have a decently collimated pair of these and I always knew about some of the mechanical / optical issues of the SkyMasters but this is really an educational experience for me reading this, so thank you all for this excellent reading material!!!

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PowellAstro
scholastic sledgehammer
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Reged: 10/14/09

Loc: Tennessee
Re: Findings with Celestron SkyMaster 15x70 binoculars new [Re: nicknacknock]
      #5981169 - 07/20/13 10:33 AM

@ GlennLeDrew

I think they did this by design. As you may know, most lens mounting cells cover the extreme edge. So, if there is a slight edge problem, it is covered by the cell. In the Skymaster 70s, the plastic cell is glued to the outside of the lens. This leaves the whole lens in the optical path. If there was to be a turned up or down edge, and most times there are, it could have a large effect. This way it is vignetted and the effect all but canceled.


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Binojunky
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Re: Findings with Celestron SkyMaster 15x70 binoculars new [Re: PowellAstro]
      #5981420 - 07/20/13 01:09 PM

To be honest if you get a good pair of Skymasters they are a great bang for the buck, I paid $50 Canadian for mine at a local store, they have lost colimation once however a tweek of the prism screws got things back in working order.
When comparing the Obies and Skymasters visually the real major difference is a brighter image and the Obies came with a better neck strap,DA.


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Scanning4Comets
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Reged: 12/26/04

Loc: Ontario, Canada
Re: Findings with Celestron SkyMaster 15x70 binoculars new [Re: Binojunky]
      #5982434 - 07/21/13 05:01 AM

Quote:

It is the front prisms that stop them down. Good news, I now have the full 70mm use of the objective lenses! I moved the lenses back in each barrel just over 1/4 inch. The center of the lenses are now flush with the outside edge of the barrels. With this I now have fully illuminated exit pupils all the way around! I can also now focus as close as 32 feet and still have a 1/3 turn left on the focus knob. I have no idea other than their lock ring setup, as to why they had the lenses screwed so far into each barrel. Mine are back together now and they look like a 500 dollars pair of binos. Images are very sharp, contrasty and with way better color saturation!

I will document all that I have done to them as soon as I can pull it all together. I am glad to answer any questions.




Excellent posts and well documented pictures to go along with it! Looking forward to more!


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PowellAstro
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Reged: 10/14/09

Loc: Tennessee
Re: Findings with Celestron SkyMaster 15x70 binoculars new [Re: Scanning4Comets]
      #5983274 - 07/21/13 04:33 PM

Update on visual use after the mods. I have a pair of 15+ year old Celestron 9x63 Ultimas which I paid 389.00 for and were made in Japan. The 15x70 Skymasters now perform just as good as the 9x63s in every respect but one. The Skymasters on Venus and the Moon show the ever slightest reflection. This is just a single reflection about 60% the size of the object and looks to be about 5% reflection. This is not a problem and you don't see it unless you are looking for it. This said, I think it is great news as it seems the most important things(optics) are of high quality. The main places where I know could be improved are the plastic eyepiece barrels and the plastic objective barrel and plastic lens cells. In the optics, it seems the only real benefit would be full multi coatings. This would remove that last small reflection seen on the brightest objects. I am very happy with the results.

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GlennLeDrew
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Re: Findings with Celestron SkyMaster 15x70 binoculars new [Re: PowellAstro]
      #5983347 - 07/21/13 05:35 PM

Just one ghost image? I recall more than one on, say, the Moon, when I had a pair of these (which I gave to an older friend.) Two things can result in the difference; rather better coatings, which I doubt, and the change in the position of the prism assembly with respect to the objective/eyepiece.

In the latter case, if a ghost results from a reflection from an eyepiece element and thence the rearmost prism face, the altered distance between the two surfaces can well result in the ghost being made angularly larger and hence more spread out and thus dimmer.

Might this be an additional benefit of moving the objectives farther out in their cells?

If I understand correctly, you report that the objective's front edge is not much masked by the 'retaining ring', which effectively provides a bit more than a 70mm clear aperture?

Have you confirmed the working aperture via the flashlight test? Is it >70mm?

Regarding turned edge problems. When present, it usually extends inward beyond the small ~1.5mm annulus masked by either the retaining ring or cell shoulder. (I had this problem in spades with a pair if 50mm f/3.3 objectives, which I fixed while performing general aspherization on the front surfaces so as to maximize performance.)


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PowellAstro
scholastic sledgehammer
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Reged: 10/14/09

Loc: Tennessee
Re: Findings with Celestron SkyMaster 15x70 binoculars new [Re: GlennLeDrew]
      #5983371 - 07/21/13 05:54 PM

In the Skymasters I have as I stated in the previous post, the lens is 70mm and the cell has no edge at all. It is like a very thin tube with threads on the outside. The lens is then glued inside this tube and there is no shoulder at all. This means the complete lens is effective right to the bevel of the glass edge. As to the reflections, I believe it may be the result of moving the lens forward. At any rate they perform great as they are now. You have to move the moon off center and really look for the ghost to even see it!

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