Binos on a Sumerian Alkaid 12"

[BillyBoyBoy]

Anybody ever used binos on a Sumerian 12"? I have a pair of Denkmeier Binotron 27s and I'm looking to acquire the scope as a travel dob. Just wondering how well it handles the weight of the binos, or not...

I have read that using more bungee cords is helpful.

Also, I see that there are two focal ratios available for the Alkaid - f/4 and f/5 - and if someone has used binos with the scope, which one might be a better choice for acquiring focus.

Thanks!

Bill 

[nicoscy]

Hi Bill,

I had a 12" f4 Sumerian but not the Alkaid (it was its slightly beefier cousin) in the past. Some feedback:

1. More bungee cords will definitely be required and the best thing is to actually email Michael of Sumerian with the weight measurement of your Binos with eyepieces and corrector so that he can inform you as to the best way to go about it.

2. There is no difference in where focusing will take place either in f4 or f5 in terms of using the scope, as depending on what you order, the trusses will be cut to the right length to facilitate focusing an eyepiece at either ratio. The decision you need to make is if you want to use the binoviewers natively or not. Using them without a corrector means that you need to let Michael know the lightpath of your binoviewers to shorten the trusses accordingly, be it f4 or f5. Binoviewers need significantly more in-travel than eyepieces due to the internal folding of light from the prisms inside.

You need to keep in mind though, that using binoviewers in native configuration and regular eyepieces, means also getting a focuser extension tube as your eyepieces will focus further away as a result. Another option is to get in touch with Harry Siebert and get one of his binoviewer zero or 1.3x OCS units for your binos.

3. F4 Vs f5. Coma becomes an annoyance for most people at anything below f5, resulting in the purchase of a Paracorr. It is up to personal preference, but I for one, always used a Paracorr with my dobs to make sure I get the best image fidelity and quality. Since you will be travelling with the scope, a Paracorr is extra weight. However, going from f4 to f5 results in longer trusses by about 30cm - so something to consider.

Hopes this helps a bit

[nicoscy]

Quick addition: F4 Vs F5: Means that the trusses are 300mm longer at f5, meaning greater torque on the bungee cords...

[Stu]

I have a 14" f4.5 Alkaid and think you may need some upgraded bungees. Mine needs both bungees fully tensioned with a 30mm ES 2" eyepiece, particular when looking low down in the sky. Nicos' point about the leverage being more on f5 than f4 is very valid. At f5 the binos will certainly need more bungee tension that at f4. Worth considering. f4.5 is quite a good compromise, although it would still benefit from a paracorr. On the counter side, eyepiece height is also likely more convenient at f5.

[nicoscy]

Re eyepiece height, I definitely needed to use an observing chair as a 12" is not a very tall Dob. Travelling though makes taking such a chair challenging, but at least something like a Walk stool might come in handy.

Scroll down the page - they come out in varying heights between 50 cm - 75cm.

[estwing]

Whole point of a travel dob is to keep weight down to bare minimum thus the materials in construction are not expecting a great chunk of glass and metal at the eyepiece.....but it's your scope, just a heads-up.

[Stu]

2 minutes ago, estwing said:

Whole point of a travel dob is to keep weight down to bare minimum thus the materials in construction are not expecting a great chunk of glass and metal at the eyepiece.....but it's your scope, just a heads-up.

True enough. My scope is certainly happier with a 24mm Panoptic than a 30mm ES, although the additional field of view is worth it.

[nicoscy]

Agree on a travel dob with lightweight accessories, but that's a personal choice. 

Bill chooses to go the whole nine yards, so any help we can provide and all...

[Nyctimene]

Hofheim Instruments offer a set of shortened tubes for their 12" f/5 traveldob, for use with a Baader binoviewer (+ correctors 1.7x or 1.25x).  No bungee cords, but a additional counterweight needed; works down to 10° elevation. The price is in a similar range as the Sumerian Alkaid 12". Have a look (only German text available):

http://www.hofheiminstruments.com/bino-stangen-set.html

No own experience with the 12" (and of course, no affiliation etc.)

Hth.

Stephan

[BillyBoyBoy]

Thank you all for your insight!

What can I say, I'm hooked on binos.  Stereo visual is just that worth it IMO.  It's just so easy to get lost in visual observation with it.  My goal isn't necessarily traveling lightweight, as much as it is being able to carry on a plane. Just the size the 12" breaks down to, being less than carry-on restrictions, is definitely what piqued my interest.  

I did get a response from Teleskop Express (the only dealer that I've found that ships to the US) that suggested I have a counterweight as well as bungee array. I'll give Michael at Sumerian a shout, too, for his thoughts on my intent with the binos.

Nicoscy, I have an OCS for the binos, and I figured I'd need it for this dob, too.  I have it for my 16" dob at home (the one that doesn't fit in the overhead compartment) with the extension tube, etc.  As far as focal ratio, it sounds like the f/5 is for me. A Paracorr is just more weight, and binos are already pushing it. I'm somewhat tall, so eyepiece height with longer poles sounds like another selling point on the f/5.  Ill check out that Walk Stool, too.  Thanks for all the info. Super helpful.

More to come when I get my responses from both Teleskop and Sumerian. 

Now please excuse me while I learn German ?

Cheers!

[BillyBoyBoy]

Guten tag!

I checked out the Hofheim 12" (thank you Stephan).  They utilize a counterweight at the bottom that is to be filled with water and or sand, which is the approach I planned on taking with the Sumerian.

Only downside is the number and size of the cases.  Two cases, which wasn't really a deal killer, as only the case with the mirrors would need carry on, but neither case has all three L x W x H dimensions less than or equal to carry on specs.  One is 9cm x 41cm x 41cm and the other is 17cm x 45cm x 50cm.  My only concern is that with carry on specs of 22cm x 35cm x 56cm, my luck the airline will fuss about being slightly over, especially on a full plane, and the risk of having to check the case will always be there.  I've read some airlines are ok with adding up the dimensions to accept a total of 115cm or less, some are more strict to the individual dimensions.  One thing I will not check is a mirror or an objective lens.  If it wasn't a dumb idea to take apart my TEC 140, I'd be traveling with that.

Digging in to learning about the Hofheim certainly led me to other dob makers that never would have shown up on my radar.

http://www.sud-dobson.fr/clemain.html 

http://www.dietermartini.de/ 

https://www.maison-astronomie.com/telescopes-dobson/3021-dobson-nadirus-12.html#/334-version_opt_monture_moteurs-with_optics 

http://www.dobsonians.co.uk/Ultra Portable.htm

Pretty neat approaches to a travel dob, though not small enough to carry on, still pretty cool.  I like the last one.  That's a serious dude right there.

More to come, including Michael's feedback from Sumerian.

Bill

[Nyctimene]

17 hours ago, BillyBoyBoy said:

My only concern is that with carry on specs of 22cm x 35cm x 56cm, my luck the airline will fuss about being slightly over, especially on a full plane, and the risk of having to check the case will always be there.  I've read some airlines are ok with adding up the dimensions to accept a total of 115cm or less, some are more strict to the individual dimensions

Replying to FAQ's, Hofheim Instruments suggest for their 12" traveldob, to go without the transport boxes in such cases. They recommend to take the primary, well protected in bubble wrap, into the hand luggage; and to store the mechanics, again without the transport box, in a well padded hard protective case. No measurements about the dimensions given; but you might contact them; very friendly and helpful people.

Stephan

[BillyBoyBoy]

10-4 will do

Thank you, Stephan.

Bill

[BillyBoyBoy]

Ok gang, I pulled the trigger.

My Sumerian Alkaid 12" f/5 should be in my hot little hands in 3 to 4 months.

The culmination of the advisement I got (thanks to y'all, Teleskop Express and Sumerian, and research I did sets me on the following path in the use of the scope with my Denk binos: 

1)  Counterweight the bottom with a sand- or water-fillable weight to travel empty of course to keep my luggage lighter.

2)  Use some greater tension bungees to work with the counterweight.

3)  Install the sensor kit for digital setting circles and utilize an Argo Navis to make the scope a push-to with a SkyBT to work with my Sky Safari on Android.

Can't wait for things to start arriving!

Bill

[Stu]

Sounds exciting Bill!

Just one question, is it worth asking Michael to cut the truss poles to a slightly shorter length so that you can use the binoviewers without OCS if wanted? Might just need to make sure the secondary size is ok but worth considering.

[BillyBoyBoy]

I've got an OCS for my binos, so I wasn't worried about coming to focus.

Just curious, why would one choose cutting the scope length vs just using an OCS?

Bill

Edited November 29, 2018 by BillyBoyBoy
Autocorrect!

[Stu]

45 minutes ago, BillyBoyBoy said:

I've got an OCS for my binos, so I wasn't worried about coming to focus.

Just curious, why would one choose cutting the scope length vs just using an OCS?

Bill

OCS adds a multiplying barlow factor so you can't use the scope at its lowest power. Minimum is usually x1.25, not sure which one you have?

If only using for mid or high power views it's not an issue.

[nicoscy]

You can always ask Harry Siebert if he has a 1 x OCA...

[Stu]

1 hour ago, nicoscy said:

You can always ask Harry Siebert if he has a 1 x OCA...

But that doesn't help if the binoviewers won't come to focus without a Barlow to push the focal point out.

[nicoscy]

Does actually. the 1x OCS extends the light path within the corrector, restoring it back to the same focal length on exiting the corrector.  Please review this and scroll down to Ad #3.

At least that's what I recall from past discussions a couple of years ago with Harry. Dropping him an email won't hurt!

[Stu]

7 minutes ago, nicoscy said:

Does actually. the 1x OCS extends the light path within the corrector, restoring it back to the same focal length on exiting the corrector.  Please review this and scroll down to Ad #3.

At least that's what I recall from past discussions a couple of years ago with Harry. Dropping him an email won't hurt!

Interesting, will have a read. I'm struggling to see how that adds back focus to compensate for the optical path length of the binoviewers? Does it do that in addition to its normal function?

[nicoscy]

I would think it does something like the image I attach. Excuse the crude drawings - I suck at this!

 

[nicoscy]

Or something similar to change the focal point without altering the focal length. The above looks like a barlow thingie - my bad.

Oh, heck, just ask the wizard (that would be Harry).

[nicoscy]

Revising it to this:

 

[nicoscy]

Yep, the above configuration maintains the light cone at its original configuration after exiting the OCA. Probably something like this.

Hmmm, Stu, this discussion is very topical. I may get into the binoviewing game again with the AP92 and 24 Pans (or ES 24mm 68° AFOV) and a 1x  OCA. The magnification would be 25,5x and the TFOV a magnificent 2.5°.

Sigh, more expenditure...