Diagonalless observing.

[Robindonne]

After reading some reviews about diagonals and the difference in mirror quality, i read a piece that described the fall in detail/quality with even the best diagonals.
Also reviewed was the difference in eyepiece/diagonal combinations.  One eyepiece would need a prism, the other a dielectric. 
So 2 nights ago i extended the tripod to maximum length, curious to see the “extra” details on jupiter etc. without a detail-absorbing diagonal.  

Wow, i never thought to see this.  

It was an anticlimax.   Even while the focustube traveled out about 20 cm? Still couldnt reach focus.   Does anyone know if it the scope or scope/eyepiece combination what causes this?    
 

i used a skywatcher 100 ed/burgass tmb 6 mm.
 

i didnt bring any other eyepieces that night so have to check if it happens with all eyepieces.  
 

Im really interested in this diagonal-less setup.  Using an adc, waiting for perfect seeing etc. to see more detail, while a simple improvement can be made by just skipping a piece of equipment.  
 

If anyone can advice me about the needed ingredients in a scope/eyepiece combination to get this to work, ill be very thankful.  

[johninderby]

A 2” diagonal adds aboit 4.5” to the light path so if viewing straight through you would need to add an extension to replace the diagonal. 

The light loss of a good diagonal is so small it is unnoticeable, about 1%. Just not worth the bother to most people and a diagonal makes it easier to look through so few people bother over here although straight through viewing is popiular in Japan.

[Robindonne]

Ah ok.  So 4,5” for the mirror?   No i completely understand the benefits over the loss of detail, when using a diagonal.  It was more because some experienced(i guess) reviewer wrote about an eyepiece not showing its potential with a dielectric and does show it with a prism and vice versa.  

if its just a case of extending the tube, then i’ll try it.    I thought it could have something to do with the eyepiece itself.  Thx

Edited August 9, 2020 by Robindonne

[johninderby]

It all depends on the scope. Shorter focal length scopes work better with a mirror diagonal and many longer focal length scopes work better with a good quality prism diagonal. 

Edited August 9, 2020 by johninderby

[JeremyS]

4 hours ago, Robindonne said:

After reading some reviews about diagonals and the difference in mirror quality, i read a piece that described the fall in detail/quality with even the best diagonals.
Also reviewed was the difference in eyepiece/diagonal combinations.  One eyepiece would need a prism, the other a dielectric. 
So 2 nights ago i extended the tripod to maximum length, curious to see the “extra” details on jupiter etc. without a detail-absorbing diagonal.  

Wow, i never thought to see this.  

It was an anticlimax.   Even while the focustube traveled out about 20 cm? Still couldnt reach focus.   Does anyone know if it the scope or scope/eyepiece combination what causes this?    
 

i used a skywatcher 100 ed/burgass tmb 6 mm.
 

i didnt bring any other eyepieces that night so have to check if it happens with all eyepieces.  
 

Im really interested in this diagonal-less setup.  Using an adc, waiting for perfect seeing etc. to see more detail, while a simple improvement can be made by just skipping a piece of equipment.  
 

If anyone can advice me about the needed ingredients in a scope/eyepiece combination to get this to work, ill be very thankful.  

Diagonal-less observing is the norm in Japan, as John Inderby says. This is one reason why Tak scopes have all that expensive back end plumbing available to accommodate different focus points. And just when I think I've got it cracked, I find another combo is required!

[andrew s]

Hum, if you use a conventional Newtonian the it will always have a diagonal!

Also close to focus angular wave front errors have less distance to generate linear errors.

A prism in a low f system will generate chromatic aberration.

I would like to see some quantitative evidence for these claims.

Certainly straining your neck or viewing in a contorted bodily position will impact your visual system.

Regards Andrew 

[JeremyS]

2 minutes ago, andrew s said:

Hum, if you use a conventional Newtonian the it will always have a diagonal!

Also close to focus angular wave front errors have less distance to generate linear errors.

A prism in a low f system will generate chromatic aberration.

I would like to see some quantitative evidence for these claims.

Certainly straining your neck or viewing in a contorted bodily position will impact your visual system.

Regards Andrew 

I should have seen that one coming 😂

[JamesF]

5 minutes ago, JeremyS said:

I should have seen that one coming 😂

Though because of the inversion you'd probably have seen it going.

James

[Robindonne]

1 hour ago, andrew s said:

Hum, if you use a conventional Newtonian the it will always have a diagonal!

Also close to focus angular wave front errors have less distance to generate linear errors.

A prism in a low f system will generate chromatic aberration.

I would like to see some quantitative evidence for these claims.

Certainly straining your neck or viewing in a contorted bodily position will impact your visual system.

Regards Andrew 

It was for me an option because im often viewing from a hammock😀.   No but serious.  I’ll try to find that review and link it here.  It basically said that one eypiece suffered from a certain type of diagonal while the another eyepiece benefits from using that type of diagonal.   It was my own conclusion that skipping this diagonal would benefit every eyepiece.   
 

And the part of that hammock was kind of serious.  I often lay down in it, and it happens to be just perfect positioned to look at the planets😬

[Robindonne]

1 hour ago, andrew s said:

Hum, if you use a conventional Newtonian the it will always have a diagonal!

Also close to focus angular wave front errors have less distance to generate linear errors.

A prism in a low f system will generate chromatic aberration.

I would like to see some quantitative evidence for these claims.

Certainly straining your neck or viewing in a contorted bodily position will impact your visual system.

Regards Andrew 

It was after reading something about a bought used eyepiece.   
 

im not an expert and dont believe immediately everything thats being written in reviews.  But sometimes you find a particular review reasonable and trustful i guess.  
 

it was this post:

https://www.cloudynights.com/topic/475997-tak-le-vs-sterling/

[John]

I use my refractors without a diagonal when I want to remove that component from the light path, eg: for star testing, collimation checking etc.

I've tried to get a collection of diagonals that have minimal negative impact on the image quality because I much prefer to have one on the scope when I'm actually observing though it !

 

[Bruce Leeroy]

9 hours ago, Robindonne said:

if its just a case of extending the tube, then i’ll try it.

If you have a barlow you could try removing the lens element and use the body as an extender, you can stack 2 or more together if 1 isn't enough or if your just mm away don't put the eyepiece all the way to the hilt. HTH

[Robindonne]

26 minutes ago, Bruce Leeroy said:

If you have a barlow you could try removing the lens element and use the body as an extender, you can stack 2 or more together if 1 isn't enough or if your just mm away don't put the eyepiece all the way to the hilt. HTH

Yes thx.  Thx for all the info btw.   Im going to play with it a bit tonight.   Was just wondering if certain eyepieces get in focus quite quickly/short vs ones that need to be more outwards(the focustube). But i guess that also varies from scope to scope.  If i suddenly see some cloudbands moving on jupiter tonight ill let you know!🙂

[John]

1 hour ago, Robindonne said:

Yes thx.  Thx for all the info btw.   Im going to play with it a bit tonight.   Was just wondering if certain eyepieces get in focus quite quickly/short vs ones that need to be more outwards(the focustube). But i guess that also varies from scope to scope.  If i suddenly see some cloudbands moving on jupiter tonight ill let you know!🙂

Not all eyepieces reach focus at the same point by any means. Not even in the same eyepiece range in some instances.

 

 

[Robindonne]

35 minutes ago, John said:

Not all eyepieces reach focus at the same point by any means. Not even in the same eyepiece range in some instances.

 

 

Ah ok.  Didn’t now that.  So if one 6 mm wont work doesn’t mean all other 6 mm’s also don’t work.   Air is too thick right now to test some.  I will soon i hope.  Thx

[Starwatcher2001]

Some eyepiece ranges are specifically designed to be "parfocal" and have the same focal point so you can swap them in and out without having to re-focus. Some do it better than others.