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Using a Mirror Diagonial with Pentax Scopes (1 Viewer)

grcolts

Member
Has anyone tried using a mirror diagonial in either the 80ED or 65ED spotting scopes? It would seem to me if one were using a straight scope by using a mirror diagonial to hold the eyepiece you would end up with an angled scope?
So, by using one of these it would be possible to have the best of both a straight and angled scope? Any reason this would not work?
GR
 
Yes, I tried already while I was trying to get my binoviewing setup to work.

The mirror diagonal adds 3 inches to the length of a scope's optical path. Without any other optics to assist, you will either not be able to focus out to infinity or not be able to come to focus at all.

The solution is the Harry Siebert 1.25x OCA. I ordered that one by mistake because I thought it would help my binoviewers come to focus. Instead, it is designed to compensate for the extra 3 inches a diagonal adds and allow eyepieces to come to focus with a mirror diagonal.

It costs $99 and consists of two lenses. The first lens labeled #2 screws into the front of the mirror diagonal. The second lens labeled #1 screws into the front of your eyepiece.

With it, you can use a 90 degree diagonal with your Pentax.

It does have two drawbacks. First, like its name, it will boost your magnification by 1.25X. The second draw back is if you want to change eyepieces, you need to unscrew lens cell #1 and screw it into the eyepiece you want to swap in.

My Pentax SMC zoom's nose doesn't have a thread (it has a sealed lens to make the eyepiece waterproof) for the cell #1 to screw into so the two aren't compatible. Other normal astro eyepieces work fine with it.

One way around the second drawback is Harry Siebert hand makes all his products. You could custom order one of his diagonal where he already builds the cell #2 into the nose of the diagonal and cell #1 into the eyepiece barrel. Then it is problem solved, just remember to throw some money at it :bounce:
 
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grcolts said:
Has anyone tried using a mirror diagonial in either the 80ED or 65ED spotting scopes? It would seem to me if one were using a straight scope by using a mirror diagonial to hold the eyepiece you would end up with an angled scope?
So, by using one of these it would be possible to have the best of both a straight and angled scope? Any reason this would not work?
GR
WOUldnt you have an upside-down image ?.a mirror diagonal turns an upside-down image upright,but it would do the opposite to an upright image...
 
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Seems like a lot of money to spend to get the "best of both." Unless you already have a straight scope, why not just get an angled one? I think that most folks who have one get used to it quickly and prefer it.
 
Upside Down Image

There are different diagonals that would not turn an image upside down.
The mirror diagonal I believe would do as you have stated.
From Can Poppers reply it sounds like the 80ED straight could work but with more money to make it do so. May be more effort than it is worth?
GR

mayoayo said:
WOUldnt you have an upside-down image ?.a mirror diagonal turns an upside-down image upright,but it would do the opposite to an upright image...
 
Best of Both Worlds

It sounds good in theory but with the logistics of making it work with a digaonal piece it does seem like a lot of money to go that route. Most likely the angled scope is in my future although there are advantages to a straight scope too. For most of my needs in a scope, I guess the angled would be the best route to go. Did anyone notice a review by Laura Erikson (sp) concerning the Pentax 80ED? She compared it to the Zeiss and Leica scopes and felt it was not in the same league with them. Funny, other reviews rate it much more highly, even going as far to suggest it may be the best scope out there for the money.
GR

RAH said:
Seems like a lot of money to spend to get the "best of both." Unless you already have a straight scope, why not just get an angled one? I think that most folks who have one get used to it quickly and prefer it.
 
Upside Down Image

There are different diagonals that would not turn an image upside down.
The mirror diagonal I believe would do as you have stated.
From Can Poppers reply it sounds like the 80ED straight could work but with more money to make it do so. May be more effort than it is worth?
GR

mayoayo said:
WOUldnt you have an upside-down image ?.a mirror diagonal turns an upside-down image upright,but it would do the opposite to an upright image...
 
grcolts said:
Has anyone tried using a mirror diagonial in either the 80ED or 65ED spotting scopes? It would seem to me if one were using a straight scope by using a mirror diagonial to hold the eyepiece you would end up with an angled scope?
So, by using one of these it would be possible to have the best of both a straight and angled scope? Any reason this would not work?
GR

By introducing additional optics into the light path I would think there would be at least some degradation of optical performance.

Considering this I would think a angled scope designed and built from the ground up for this purpose at the factory would be optically and mechanically superior to any third party add-on.
 
grcolts said:
Did anyone notice a review by Laura Erikson (sp) concerning the Pentax 80ED? She compared it to the Zeiss and Leica scopes and felt it was not in the same league with them. Funny, other reviews rate it much more highly, even going as far to suggest it may be the best scope out there for the money.
GR

Often the difference in the perception of quality by reviewers is blamed on a lack of quality control by the manufacturers.

More and more I think the real lack of quality control may be in the selection of who does and does not evaluate these products.

I take all opinions, including my own, with a grain of salt.
 
grcolts said:
It sounds good in theory but with the logistics of making it work with a digaonal piece it does seem like a lot of money to go that route. Most likely the angled scope is in my future although there are advantages to a straight scope too. For most of my needs in a scope, I guess the angled would be the best route to go. Did anyone notice a review by Laura Erikson (sp) concerning the Pentax 80ED? She compared it to the Zeiss and Leica scopes and felt it was not in the same league with them. Funny, other reviews rate it much more highly, even going as far to suggest it may be the best scope out there for the money.
GR

It all depends on each person's circumstance. If you are like Medinabrit with all three Pentaxes (65, 80, 100), then the cost of such a mod gets spread between multiple scopes.

Or if you are a person with an good astro scope and a Pentax spotter, the OCA and diagonal can be just reused components.

But if a Pentax 65ED is your only scope, the $200 for a dielectric diagonal plus OCA could be half the price of the scope.

Is the Laura Erikson you are refering to the one on binoculars.org? If so, it wasn't a completely fair comparison. For the Pentax, she used the SMC zoom while for the other scopes she used fixed eyepieces (notice for Zeiss she used the 30x and 40x fixed ep's). The guy here also made the same mistake: http://www.6mmbr.com/spotterreview.html. To get a truly fair comparison, they should use equivalent quality fixed eyepieces on the scopes to determine the winner. Instead, both are apples to oranges comparison rookie mistakes.

The Pentax SMC does have the problem of the eyerelief feeling shorter than listed thus making it hard to digiscope. This is what may have turned Laura off. However, most of the Pentax fixed ep's do not (nor do many of the other astro choices available).
 
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grcolts said:
There are different diagonals that would not turn an image upside down.
GR

There are no diagonals that wouldn't invert the image. Possibly you are thinking of Amici or Schmidt diagonals which would invert the image, just like a mirror, but not reverse right and left.
 
Sout Fork said:
Often the difference in the perception of quality by reviewers is blamed on a lack of quality control by the manufacturers.

More and more I think the real lack of quality control may be in the selection of who does and does not evaluate these products.

I take all opinions, including my own, with a grain of salt.

The sample variation in birding scopes is quite real. A quick star test at 60X is all it takes to show the optical defects that can turn up even in the expensive ones.

Reviewers who don't star test the scopes they are reviewing really can't tell whether an optical problem they see in the image is a design flaw or a sample defect.
 
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henry link said:
The sample variation in birding scopes is quite real. .

I don't doubt it for a moment.

Having said that we are still left with the problem of not only judging which optics to buy but, even more problematic, who is competent to give an opinion on optical performance in the first place.
 
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