657 replies to this topic

[clamchip]

Here's the Zeppelin.

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[clamchip]

I got an idea how close the collimation is with defocused Christmas lights!

 

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[clamchip]

It stopped raining so now the trails can begin to see if the Edmund 5 inch lens moves on to a permanent tube,

or goes back in the shortbread tin.

I'm a little worried about the f/14.2 focal ratio and CA, and these worries were intensified when I was observing my

neighbors Christmas lights and I was horrified by the brilliant neon purple fringe. This was while defocused because

I was just looking at diffraction rings to see if the lens was roughly collimated. And also since the lights were not at infinite focus the lens would be over corrected.

I don't know a whole lot about lenses, I do have some excellent books in my library I can consult as the information starts coming in.

I'll start with my usual daytime targets and hopefully the sun will appear so I can get some glints from power line insulators

and car bumpers.

 

Robert

[Joe1950]

I'm not an expert on lenses/optics Robert, but I believe the out of focus image will show definite color rings, which are different inside focus and outside focus. That is normal for an achromat. And, I believe the noticeable CA at focus will be worse if the scope is out of collimation.

 

It's been recommended that if you are doing a star test on a refractor to assess the quality of the lens figure, you should use a green filter so that the color differences do not confuse the issues.

 

Your scope is very close to the Sidgwick standard and will likely show low-moderate CA, depending on what you are viewing. I've noticed on my short focus reractor, the CA seems much worse on daytime objects than it does on stars and planets at a given magnification. Some of the holiday lights have very high brightness levels and could be misleading. Even telephone pole insulators and branches are seen at a high contrast level and the CA is readily visible. I saw that with my 3", f/6.25.

 

But when I looked at Vega, the purple glow was not really bad at all. Just noticable, and it didn't extend far. Again when I collimated the scope better, the CA seemed to be significantly less.

 

Maybe someone with much more knowledge can comment.

 

Keep us posted, Robert. I have no doubt the scope will be superb! Remember, Galileo used a refractor, not a Newt or a CAT, so that says something right there! 

 

joe

Edited by Joe1950, 13 December 2015 - 02:07 PM.

[clamchip]

The 5 inch lens isn't blowing my socks off like the 4 inch Edmund, I'm going to need lots more time.

I did find an interesting condition the scope was suffering from that I've never run across, I'm

going to call it "lens flop". The lens retainers were loose enough to allow the elements to move away from

each other when the telescope was horizontal, losing the all important correct air space between the elements. 

I would start moving the telescope to zenith until I heard the soft little "toonk" and then the image in the

eyepiece was super sharp!

You should have a small amount of rattle, the elements in the cell when shaken.

 

Robert

Edited by actionhac, 13 December 2015 - 06:14 PM.

[TSSClay]

Robert,

 

Could you maybe put an o-ring under the lens retaining ring?  I am designing a cell for a 6" f10 and I am going to see if I can get an o-ring groove in the end of the threaded retainer to gently hold the lenses yet allow some compliance for expansion and contraction.

 

Clay

[Joe1950]

Just as I was typing, Clay!!! A little different approach but essentially the same concept.

 

I've heard that many times as being done with both refractors and reflectors, Robert, but I never really liked the idea. 

 

As you have noticed the lens spacing can change. Also, given enough free movement over time, one element may rotate relative to the other. And finally, with all the emphasis put on properly collimating a scope, how can it stay that way if the lens, or mirror is rattling around?

 

So, this is what I've done. I get "O" rings, used in plumbing that are about the thickness of the lens retaining ring. I'll get 2 or 3 rings. On refractors, I'll loosen the retaining ring about to about the thickness of the O-rings, being careful not to cause the forward element to rotate relative the rear element as I turn the retaining ring. I wear latex gloves and hold the front element in place. It's good if you have and can see indexing marks on the lens edges.

 

I'll take the O-rings and cut them so that I have 3 - 2" lengths. The length is not critical. On a large lens like your 5" which has over a 16" circumference, you might want to use 3" lengths.

 

Taking the 3 O-ring lengths, I slip them under the retaining ring at equal intervals around the circumference. If they pop out or don't stay in place, I turn the retaining ring in a little so that the O-rings just fit in the gap between the retaining ring and the lens.

 

Again, holding the front lens so as not to rotate, I tighten the retaining ring so that it is snug, but not real tight.

 

This keeps the lens in place yet allows for contraction of the cell on the lens without pinching the optics because of the elasticity of the O-rings.

 

It has worked very well for me and I am not concerned with the lens being squeezed by the cell, or the lenses flopping around unnecessarily. Some manufactured scopes have the lens ring tightened so tight it's like having a vice-grip on them. 

 

Most of the mirror cells have cork or rubber pads under the mirror and on the mirror clips for the same reason.

 

Just an idea. 

Edited by Joe1950, 13 December 2015 - 07:35 PM.

[clamchip]

I like the O ring idea you guys.

Thats a great idea because it will be snug and not rattly so the air-space won't 

change. The Edmund 5 inch lens doesn't have a retaining ring it has these 3 blocks 120 deg apart that

I've marked here in this picture. I can still use your guys's O ring idea by gluing O ring pieces to the

blocks, normally thin felt goes in these locations.

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Edited by actionhac, 13 December 2015 - 08:40 PM.

[Joe1950]

Brilliant, Robert!  That cell is made for a mod such as that. It's no different than a mirror cell with three metal clips and rubber or cork on the clips to allow for contraction.

 

joe

[clamchip]

Its been raining day and night so I haven't had much observing time with the Edmund 5.

I have been working on the mechanics of the scope and thought I would finish  the

telescope the way I think Edmund would have offered it if it had ever gone into production.

I'm sure Edmund would have sold the 5 with the Deluxe finder. The Deluxe finder is an

impressive instrument with its 12 deg field. Weight as shown in these pictures is exactly 3lbs.

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[clamchip]

This will be the first time I've used the Deluxe finder on a telescope and

I thought it would be a good idea to have a safety wire to prevent the  

finder from sliding out of the rings, you may be able to see the safety in

this photo, from the brass focus thumb screw to the nylon ring screw.

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[clamchip]

I'm using a felt lined pill bottle for a dew shield.

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[catboat]

Robert,

 

That Deluxe finder looks stunning.  You stripped and polished the tube, yes?  

 

I have the same finder and bracket.  The bracket’s a beauty in its own right.  I’m waiting (years now) on the time when I’ll assemble a scope big enough to justify the weight.  In the meantime, I could happily occupy myself with stripping the original paint and mitigate color-coordiantion decisions…      Yours is a looker.

[clamchip]

I bought it polished like it is but I can see circular marks from the ring screws that

were there before it was polished so the marks must have been pretty deep and

didn't get completely sanded away.

I agree the bracket is quite a casting.

This is the kind of stuff I really like and is a big part of why I like Edmund Scientific so much.

 

Robert

Edited by actionhac, 18 December 2015 - 12:01 PM.

[Edward E]

This will be the first time I've used the Deluxe finder on a telescope and

I thought it would be a good idea to have a safety wire to prevent the  

finder from sliding out of the rings, you may be able to see the safety in

this photo, from the brass focus thumb screw to the nylon ring screw.

This is the first time I have seen someone else with this finder.  I figure that there are not many out there in circulation anymore.  These are great finders and work very well with the free Deep Sky Watch atlas from Michael Vlasov.  I like your DIY dew shade; does that help with contrast?  If so, I will have to make one for my finder.

[clamchip]

The pill bottle shade works very well for dew, I haven't tested it for contrast improvement but I'm sure

it probably will improve stray light control since the objective is so unprotected. 

The objective lens right out at the edge of the tube probably comes from its satellite scope ancestry,

where a first surface diagonal mirror was in front of it for comfortable satellite watching.

The Edmund Deluxe finder goes way back into the 1950's and started out life as a project moonwatch

satellite telescope.

It was available as a catalog item and standard equipment on the 8 inch reflector.

Back in the 1950's if you were the owner of the satellite scope you could buy the 2-ring finder

mount and use your satellite scope as a wide-field finder.

Here's some 1957 prices:

Satellite Telescope #70,074 $49.50 

Twin Ring Finder Mount #70,079 $9.95

Deluxe Finder with Twin Ring Finder Mount Included #70,175 $32.50

 

Robert

[clamchip]

I still have not been able to try out the Edmund 5 due to cloud cover.

I have plenty of daytime observing under my belt and the scope is sharp and capable

of very high power.

It is hard on the Unistar/Losmandy mount, mostly because of the torque of

the long tube. It will eventually go on my Edmund Extra Heavy Duty with 1-1/2" inch

shafts.

I thought a little nose art would help dress up the raw aluminum tube for now.

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[clamchip]

I installed the Edmund Deluxe finder with a pipe clamp while I decide on the final

location for it.

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[clamchip]

The 3 pound finder moves the main scope's eyepiece closer to the mount for balance which

is great.

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[clamchip]

You can see the difference without the finder.

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[Terra Nova]

Love that finder! A telescope with 'noseart'!? Who woulda thunk?!

[clamchip]

Its a great finder. The field of view takes your breath away and the very precision

glass reticle cross hairs are really nice.

The nose art comes from the fact that every time I look at the aluminum tube I think of

military aircraft and nose art. I was thinking about doing it up like a SAC B-52! but I changed

my mind.

I have a feeling this scope as neat as it is is going back in the shortbread tin.

It is a massive thing and heavy, and hard on mounts for a gain of only one inch aperture

over the extremely fine Edmund 4 inch f/15.

Also the 6 inch f/8 Edmund Super Space Conqueror is an inch larger in aperture and much

more user friendly.

So unless this 5 inch f/14.2 is so much better then those two to make it worth the extra effort

this project "Edmund 5" will be canceled.

 

Robert

Edited by actionhac, 29 December 2015 - 08:39 PM.

[Joe1950]

The long tubes are a challenge, Robert, but often the views are extraordinary!

 

I envision the refractor on a mount like the gentleman in China made for his fracts...a refractor DOB type if the HD mount makes the whole thing too heavy to handle. They seem robust and stable. With your skills, you could have one made in no time!

 

So before you return the tube to your heating system, I hope you give 5" a good look-see. Norman would like that.

Edited by Joe1950, 29 December 2015 - 10:19 PM.

[Terra Nova]

"The nose art comes from the fact that every time I look at the aluminum tube I think of
military aircraft and nose art. I was thinking about doing it up like a SAC B-52!"

A B52? Well the B52s were a great band but For nose art about this famous second to one B29?

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[Joe1950]

There you go! And the '29 has a lens, of sorts, on the front.