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Victor Boesen

Would the Takahashi prism diagonal work with f/5.8 Skywatcher evostar?

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I've read so many good things about this diagonal and struggle to find a mirror diagonal just as popular and affordable. I've heard a prism diagonal would be a bad choice with scopes under f/7 and it has had me searching the web for other solutions but I haven't found any real contester to the Takahashi. My question is if the Takahashi prism will work fine with the Skywatcher evostar 72 or if you can recommend any other 1,25" diagonal preferably from FLO or Teleskop-express??

Thank you

Victor

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Posted (edited)

Well, I'm no authority on this, but I do very happily use the Tak prism with a TV-60 at f/6 and with a Borg 71FL at f/5.6. Whether I'm seeing and just not minding what others seem not to like - or not - I don't know. The one thing to keep in mind is that the Tak prism has a relatively short path; I need an extension tube to reach focus with the Borg with its short-travel focuser (the TV-60 has a nice long drawtube).

DSC_2448.thumb.JPG.9dd0e608a013f7ecbe34ac12d0d4d74f.JPG

You can see here (with a TV-85) how I use a Baader adapter on top of the Tak prism both to lengthen the path and avoid having to use the prism's turn-all-night-long-and-snag-the-safety-undercut locking mechanism. The adapter is T2 threaded on the bottom and has a T2-1.25" adapter screwed onto it which inserts into the prism; it remains on the prism when not in use.

:happy11:

EDIT: a few pics to clarify

DSC_2776.thumb.JPG.bdbb57a6a918610d4f72748397232693.JPG

DSC_2777.thumb.JPG.a507ed2142812a164415623b5dc918e8.JPG

DSC_2778.thumb.JPG.74e505ffbb447f04eb4ee914212f6e4d.JPG

DSC_2779.thumb.JPG.66022438b52c5f9e533a9aa554a5ee01.JPG

DSC_2780.thumb.JPG.bf5e2d0811be288c90eb4ee55dedb299.JPG

...and the part numbers are:

DSC_2781.thumb.JPG.67ecb5a0f3be9d02b9579d98adb40a46.JPG

DSC_2782.thumb.JPG.133506b6b7784bfd11f4ce8cadd68db1.JPG

Edited by iPeace
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Hi Victor, I do believe that the Baader Zeiss spec prisms are genuine rivals to the Tak or perhaps any other. They are certainly better in terms of scatter and contrast than the AstroPhysics Maxbright mirror dielectric I used to have. When I’d tried the Baader prisms I sold the AstroPhysics. I have both the 2” and 1.25” Baader Zeiss prisms and use them with my TEC 140 which is an f7 apo triplet. The optical quality is exceptional. The Baader system has several other advantages, notably the very convenient clicklock arrangement.  I can’t comment on whether scopes below f7 do better with a mirror over a prism. Certainly, at f7, the Baader Zeiss prisms outperform the Baader t2 mirror diagonal that came with the Mk V binoviewer I bought some years ago.  

Bill Paolini reviewed several diagonals, including, I think, the Tak and both the Baaders. Here’s the link. https://www.cloudynights.com/articles/cat/articles/mirror-vs-dielectric-vs-prism-diagonal-comparison-r2877

... not to be confused with his review of the BBHS mirror diagonal, which is also on that site somewhere. If you wanted a mirror, those might be worth a look.

Hope this provides some useful food for thought 😊

John

 

 

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At worst you might see a fraction more CA in the Tak Prism, but I reckon it would probably be well worth a shot.

I do have a Tal Prism and a TS 72mm apo which is very similar to the 72ED so I will give them a go if i get a chance.

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22 minutes ago, iPeace said:

Well, I'm no authority on this, but I do very happily use the Tak prism with a TV-60 at f/6 and with a Borg 71FL at f/5.6. Whether I'm seeing and just not minding what others seem not to like - or not - I don't know. The one thing to keep in mind is that the Tak prism has a relatively short path; I need an extension tube to reach focus with the Borg with its short-travel focuser (the TV-60 has a nice long drawtube).

DSC_2448.thumb.JPG.9dd0e608a013f7ecbe34ac12d0d4d74f.JPG

You can see here (with a TV-85) how I use a Baader adapter on top of the Tak prism both to lengthen the path and avoid having to use the prism's turn-all-night-long-and-snag-the-safety-undercut locking mechanism. The adapter is T2 threaded on the bottom and has a T2-1.25" adapter screwed onto it which inserts into the prism; it remains on the prism when not in use.

:happy11:

The short path might be an advantage when using it with the Evostar since people only seem to have focus issues with inwards travel:) Thank you very much for your opinion and experience!

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14 minutes ago, JTEC said:

Hi Victor, I do believe that the Baader Zeiss spec prisms are genuine rivals to the Tak or perhaps any other. They are certainly better in terms of scatter and contrast than the AstroPhysics Maxbright mirror dielectric I used to have. When I’d tried the Baader prisms I sold the AstroPhysics. I have both the 2” and 1.25” Baader Zeiss prisms and use them with my TEC 140 which is an f7 apo triplet. The optical quality is exceptional. The Baader system has several other advantages, notably the very convenient clicklock arrangement.  I can’t comment on whether scopes below f7 do better with a mirror over a prism. Certainly, at f7, the Baader Zeiss prisms outperform the Baader t2 mirror diagonal that came with the Mk V binoviewer I bought some years ago.  

Bill Paolini reviewed several diagonals, including, I think, the Tak and both the Baaders. Here’s the link. https://www.cloudynights.com/articles/cat/articles/mirror-vs-dielectric-vs-prism-diagonal-comparison-r2877

... not to be confused with his review of the BBHS mirror diagonal, which is also on that site somewhere. If you wanted a mirror, those might be worth a look.

Hope this provides some useful food for thought 😊

John

 

 

Thank you very much!! I'll have a read:)

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10 minutes ago, Stu said:

At worst you might see a fraction more CA in the Tak Prism, but I reckon it would probably be well worth a shot.

I do have a Tal Prism and a TS 72mm apo which is very similar to the 72ED so I will give them a go if i get a chance.

Thank you Stu!

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Posted (edited)

I"ve got the Tak prism diagonal and it's worked well for me at f/7.5.  I think it would be fine at shorter f-ratios.  Keep in mind the length of the glass path of a prism diagonal is what determines how much color error it adds.  The Tak 1.25 diagonal probably has a very short path - as someone pointed out.   The T2-size prisms from Baader will have longer path and actually introduce more color error.  

But in general the color error is only an issue in big 2" prism diagonals that have a 4 inches of light travel through the prism glass.     I believe the Baader t-2 is only a 2-inch light path?   something like that.  So the Tak is probably even shorter.

It should be said the weak point of the Tak diagonal is the plastic twist-collet used to hold eyepieces.  It's a little weaker than metal compression ring clamps.  It's not great with big & heavy eyepieces.  Some people don't like it.   It works well enough for me.  It's perfect for small grab-n-go refractors where you're trying to keep the size and weight to a minumum.

Edited by Scott42
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25 minutes ago, Scott42 said:

It should be said the weak point of the Tak diagonal is the plastic twist-collet used to hold eyepieces.  It's a little weaker than metal compression ring clamps

That's true. It's not ideal but works well with small eyepieces. I found it catches on eyepieces with undercuts. It was a problem with my 24mm Panoptic so I ended up putting a wrap or two of insulating tape to fill the gap and that solved the problem. It grips well though.

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49 minutes ago, Scott42 said:

I"ve got the Tak prism diagonal and it's worked well for me at f/7.5.  I think it would be fine at shorter f-ratios.  Keep in mind the length of the glass path of a prism diagonal is what determines how much color error it adds.  The Tak 1.25 diagonal probably has a very short path - as someone pointed out.   The T2-size prisms from Baader will have longer path and actually introduce more color error.  

But in general the color error is only an issue in big 2" prism diagonals that have a 4 inches of light travel through the prism glass.     I believe the Baader t-2 is only a 2-inch light path?   something like that.  So the Tak is probably even shorter.

It should be said the weak point of the Tak diagonal is the plastic twist-collet used to hold eyepieces.  It's a little weaker than metal compression ring clamps.  It's not great with big & heavy eyepieces.  Some people don't like it.   It works well enough for me.  It's perfect for small grab-n-go refractors where you're trying to keep the size and weight to a minumum.

Thanks for mentioning. I purchased everything this morning so now I'm just waiting:). I'll only be using it with my 1,25" explorer scientific 82 degrees which I guess aren't too heavy with the heaviest one being 305g.

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IMO the optics are first-class in the Tak prism, I've had mine for many years with no plans to give it up.  I keep it in my eyepiece case all the time as a backup, in case something disastrous happens to my 2" diagonal during remote observing trips.   Stu's right about the collet catching on eyepiece undercuts, you must use a little more attention when changing eyepieces.

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I've used a tak prism on f5 achromats and it worked fine. These days I only use mirror diagonals in fast scopes but that's only because of the theory not because I notice any disadvantage in the field  to my eye.

The tak prism diagonal is also useful  to have in your arsenal sometimes when you are having problems with getting enough  in focus travel.

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Posted (edited)

I used Tak prism with SW 72ed, Bresser 102xs (f4.5) and ST-80. Worked fine. I didn't have anything in the mirror department to compare but it was fine. If anything the Tak prism will be better than some low-end mirror.

2 hours ago, Paz said:

I've used a tak prism on f5 achromats and it worked fine. These days I only use mirror diagonals in fast scopes but that's only because of the theory not because I notice any disadvantage in the field  to my eye.

The tak prism diagonal is also useful  to have in your arsenal sometimes when you are having problems with getting enough  in focus travel.

This! I even went ahead and bought what looks to be the best readily available mirror - Baader T2 BBHS - expensive little thing - costs exactly the same with nosepiece and eyepiece clamp as SW 72ed LOL. The other day I was comparing it to the stock Celestron diagonal that comes with C8. Maybe, just maybe the Moon was a little more contrasty. Ah, who am I kidding....if you put me in front of both and do a blind test I am not sure I would note any difference. This may be my unexperienced eye and down the road I might say differently but it is what it is now. On the other hand when I compared Tak prism, Baader T2 prism (non-Zeiss) and SW stock cheapo mirror diagonal the difference was more pronounced.

Edited by heliumstar
added content
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I've made a separate topic as an ongoing review of the scope, mount, diagonal etc which you can follow here:

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Bump - a friend on SGL asked for the particulars concerning the use of a Baader adapter to lengthen the path and avoid using the Tak prism's clamping mechanism; I've edited my post above to share with anyone interested.

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20 minutes ago, iPeace said:

Bump - a friend on SGL asked for the particulars concerning the use of a Baader adapter to lengthen the path and avoid using the Tak prism's clamping mechanism; I've edited my post above to share with anyone interested.

Thanks for the heads-up! very useful.

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On 06/08/2019 at 22:47, iPeace said:

Well, I'm no authority on this, but I do very happily use the Tak prism with a TV-60 at f/6 and with a Borg 71FL at f/5.6. Whether I'm seeing and just not minding what others seem not to like - or not - I don't know. The one thing to keep in mind is that the Tak prism has a relatively short path; I need an extension tube to reach focus with the Borg with its short-travel focuser (the TV-60 has a nice long drawtube).

DSC_2448.thumb.JPG.9dd0e608a013f7ecbe34ac12d0d4d74f.JPG

You can see here (with a TV-85) how I use a Baader adapter on top of the Tak prism both to lengthen the path and avoid having to use the prism's turn-all-night-long-and-snag-the-safety-undercut locking mechanism. The adapter is T2 threaded on the bottom and has a T2-1.25" adapter screwed onto it which inserts into the prism; it remains on the prism when not in use.

:happy11:

EDIT: a few pics to clarify

DSC_2776.thumb.JPG.bdbb57a6a918610d4f72748397232693.JPG

DSC_2777.thumb.JPG.a507ed2142812a164415623b5dc918e8.JPG

DSC_2778.thumb.JPG.74e505ffbb447f04eb4ee914212f6e4d.JPG

DSC_2779.thumb.JPG.66022438b52c5f9e533a9aa554a5ee01.JPG

DSC_2780.thumb.JPG.bf5e2d0811be288c90eb4ee55dedb299.JPG

...and the part numbers are:

DSC_2781.thumb.JPG.67ecb5a0f3be9d02b9579d98adb40a46.JPG

DSC_2782.thumb.JPG.133506b6b7784bfd11f4ce8cadd68db1.JPG

@iPeace I'm looking to buy these parts for my diagonal but I already have a nosepiece that screws into my M42 thread. Would the reducer thread allow this??? I assume it accepts both because of the (Incl. T-2 threads). And, would any other 2" to 1.25" adapter work with it?? I ask this because I need a shot light path otherwise it won't reach focus so a low profile 2"-1.25" adapter would be ideal. How far is the optical length of the entire reducer??

Victor

Edited by Victor Boesen

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2 hours ago, Victor Boesen said:

@iPeace I'm looking to buy these parts for my diagonal but I already have a nosepiece that screws into my M42 thread. Would the reducer thread allow this??? I assume it accepts both because of the (Incl. T-2 threads). And, would any other 2" to 1.25" adapter work with it?? I ask this because I need a shot light path otherwise it won't reach focus so a low profile 2"-1.25" adapter would be ideal. How far is the optical length of the entire reducer??

Victor

I'm travelling abroad for a few more days; will do my best for you when I get back.

Off hand, I assume the shortest light path would be obtained by just using the diagonal without any additional parts? Do you actually need the Baader bits? I need them to lengthen the path for use with my Borg refractor.

Edited by iPeace
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9 hours ago, iPeace said:

I'm travelling abroad for a few more days; will do my best for you when I get back.

Off hand, I assume the shortest light path would be obtained by just using the diagonal without any additional parts? Do you actually need the Baader bits? I need them to lengthen the path for use with my Borg refractor.

Thank you very much! The reason I am looking to buy it is because of the locking mechanism. My ES 82 degree oculars all have an undercut to them and I can't lock them completely tight(without mentioning how much turning I have to do after). I could look into other clicklock options that have a shorter lightpath.

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On 23/09/2019 at 07:36, Victor Boesen said:

Thank you very much! The reason I am looking to buy it is because of the locking mechanism. My ES 82 degree oculars all have an undercut to them and I can't lock them completely tight(without mentioning how much turning I have to do after). I could look into other clicklock options that have a shorter lightpath.

Apologies for the delay. I will only be able to measure approximately (hopefully tomorrow), so I hope that will be of use. Alternatively, you could wind some narrow isolation tape around the eyepiece to fill in the undercut just enough (I understand if you don't want to do this, it's just a suggestion). I think other SGL friends have done similar things to solve this problem.

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7 hours ago, iPeace said:

Apologies for the delay. I will only be able to measure approximately (hopefully tomorrow), so I hope that will be of use. Alternatively, you could wind some narrow isolation tape around the eyepiece to fill in the undercut just enough (I understand if you don't want to do this, it's just a suggestion). I think other SGL friends have done similar things to solve this problem.

Everything helps;) I've also seen a thread posted recently about the undercuts on eyepieces and I think I will probably give some electrical tape a go.

Thanks in advance!

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The problem is that any “soft” filler catches the retaining screw or jambs in the locking ring.

It really is a PITA......

 

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14 hours ago, Victor Boesen said:

Everything helps;) I've also seen a thread posted recently about the undercuts on eyepieces and I think I will probably give some electrical tape a go.

Thanks in advance!

Well, the best I can measure gives a result of 3.8 cm added to the path, perhaps 1-2 mm more. Not exactly compact...but, as stated, the added length is a feature for me, not an issue.

:happy11:

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14 hours ago, iPeace said:

Well, the best I can measure gives a result of 3.8 cm added to the path, perhaps 1-2 mm more. Not exactly compact...but, as stated, the added length is a feature for me, not an issue.

:happy11:

thank you:) I will give it one more thought before ordering.

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