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Tips for a soon-to-be 25" Obsession Owner?

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#1 Yogurthawk

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Posted 16 January 2020 - 11:02 PM

As the title suggests, by some incredibly holy and lucky manner I will soon be receiving a 25" Obsession Dobsonian. 

 

To be honest, I'm a little overwhelmed as I've never even used a scope so large and only looked through one once at a local observatory. Most of my experience is with doing astrophotography with a small refractor and more recently with a 9.25" SCT. Do you guys have any advice on:

1. Expectations

2. Observing Practices 

3. Accessories/Essentials

4. Transportation/Storage

5. The possibility of astrophotography through it?

 

Thanks for reading.

 



#2 TOMDEY

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Posted 16 January 2020 - 11:22 PM

I used a nice 29-incher for over twenty years, and am now enjoying my 36-incher. Well, you will be able to pull in a lot more stuff; aperture indeed rules, provided your skies are nice and dark. Coma corrector, of course. Transportation... I'd say to seriously, very seriously consider finding a semi-permanent observing site... even if it means just rolling out of a shed. Toting the thing afield setting up / tearing down gets very old very fast. Imagery --- put it off, preferably forever. If you feel that you must image, consider EAA or Night vision to e.g. Smartphone.

 

Enjoying the capability of biggish aperture is the goal. Anything that can defuse it becoming a chore will be to your benefit!   Tom


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#3 ShaulaB

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Posted 17 January 2020 - 12:02 AM

The collimation technique for Obsession Dobsonians is a bit different than collimation for other brands of Dobs.

 

One CN thread is here. https://www.cloudyni...in-collimation/

 

You might want to search the forums or Google for other tidbits.



#4 Astro-Master

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Posted 17 January 2020 - 12:04 AM

My friend has a Obsession 25" F/5, its a beast compared to my Obsession 18" F4.5.  He hauls it around and stores it in a Well Cargo Trailer.  You'll also need a good ladder.

 

What F Ratio is your 25", F/4 is a 2 feet shorter than an F/5, and is a little easer to manage in my opinion, and the shorter focal length will give you a wider field of view.


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#5 Codbear

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Posted 17 January 2020 - 12:15 AM

I used a nice 29-incher for over twenty years, and am now enjoying my 36-incher. Well, you will be able to pull in a lot more stuff; aperture indeed rules, provided your skies are nice and dark. Coma corrector, of course. Transportation... I'd say to seriously, very seriously consider finding a semi-permanent observing site... even if it means just rolling out of a shed. Toting the thing afield setting up / tearing down gets very old very fast. Imagery --- put it off, preferably forever. If you feel that you must image, consider EAA or Night vision to e.g. Smartphone.

 

Enjoying the capability of biggish aperture is the goal. Anything that can defuse it becoming a chore will be to your benefit!   Tom

You can't get much better advice on this than from Tom. I read up on his threads dealing with large scopes and I soaked up invaluable advice and recommendations.

 

The only reason I have a 24" SpicaEye is BECAUSE it is housed in a rollaway shed that our contractor built to be extremely easy for me to use due to my muscle disease. Open the doors, roll the shed back and it's ready to acclimate.

 

I went all out and got the GoTo with Argo Navis, which sometimes I use and sometimes I don't...it depends on what I will be looking at on any given night...and there is a LOT to look at.

 

For me personally, since my observing time is limited due to leg fatigue, I can pop off 20 objects in an our with GoTo. On the other hand, I may want to spend 20 minutes observing a glob, in which case the tracking is invaluable for me.

 

M57 with the easy central star and bluish-grey appearance, M13 with more stars than I know what to do with, Stephan's Quintet...the list goes on and on.

 

We have had a lot of bad weather so I have been saving M42 for a top notch night of transparency because I know my socks will be blown off.

 

Also be prepared to be seeing limited a lot though! You need exceptional seeing to be able to crank up the magnification to take full advantage of the mirror size. I've had mine for about 6 months and the most I've been able to crank it up to is about 400x on globs. The planets are simply too low for me to be able to get the kind of views I can get with my TEC180, because of the mirror size.

 

But I am not complaining in the least. I got the 24" for DSOs and that is exactly what it excels spectacularly at!



#6 Yogurthawk

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Posted 17 January 2020 - 12:33 AM

My friend has a Obsession 25" F/5, its a beast compared to my Obsession 18" F4.5.  He hauls it around and stores it in a Well Cargo Trailer.  You'll also need a good ladder.

 

What F Ratio is your 25", F/4 is a 2 feet shorter than an F/5, and is a little easer to manage in my opinion, and the shorter focal length will give you a wider field of view.

I do believe it's an F/5, perhaps unfortunately!



#7 Yogurthawk

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Posted 17 January 2020 - 12:36 AM

I used a nice 29-incher for over twenty years, and am now enjoying my 36-incher. Well, you will be able to pull in a lot more stuff; aperture indeed rules, provided your skies are nice and dark. Coma corrector, of course. Transportation... I'd say to seriously, very seriously consider finding a semi-permanent observing site... even if it means just rolling out of a shed. Toting the thing afield setting up / tearing down gets very old very fast. Imagery --- put it off, preferably forever. If you feel that you must image, consider EAA or Night vision to e.g. Smartphone.

 

Enjoying the capability of biggish aperture is the goal. Anything that can defuse it becoming a chore will be to your benefit!   Tom

I spend most of my time in LA for school, so the scope will be going back to my home in Arizona, but unfortunately I live in the suburbs of Phoenix (Bortle 8-9). I'm within an hour of great, dark skies but I don't doubt that transportation and assembly is very fun at all so I'm a little torn on what to do.



#8 Jon Isaacs

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Posted 17 January 2020 - 02:51 AM

I do believe it's an F/5, perhaps unfortunately!

 

I owned a 25 inch inch F/5 Obsession for about 6 years.  A wonderful scope that provided many memorable views.  I'm fortunate because  could leave the scope setup and just roll it in and out of the garage.  I never took it apart.. 

 

My suggestion:

 

Don't cut corners with the ladder.  These scopes are tall and trying to use a step ladder is not only risky but it takes away from the joy of observing. With a step ladder, you are always having to hold onto the ladder with one hand so swapping eyepieces etc and just tracking is awkward.  And they'll be a lot of trips up and down the ladder.  I am 6 feet tall, this is what I look like on a step ladder.

 

5910770-Obsession and Jon at Jewel Valley.jpg
 
It wasn't long after I got the scope that I realized I needed a better ladder.  I ended up buying a Cotterman Rolling Folding Ladder.  It made a world of difference. It has wider, deeper steps, a shallower angle, easier to climb.  It had railings on both sides and a top platform., It was comfortable and I could lean against the railings so I didn't always need to be hanging on with one hand.  I built a tray for eyepieces an accessories so I always had everything at my finger tips, no need to climb up and down the ladder.  
 
Obsession with Rolling Ladder CN.jpg
 
These scopes cost real money.  New they were around $10,000 or so.  A $10,000 scope with a $100 ladder doesn't make sense.  A good ladder is the key to comfort and safety.  If you will be transporting the scope, spend the money on an aluminum ladder but get one with rails and wheels.  
 
When was closing in on 70, I decided observing alone 50 miles from the nearest urgent care no longer made sense so I downsized to a 22 inch F/4.4.  I sold the Obsession to a young guy and he just loaded the ladder on top of his Ford Transit van.. 
 
obsession sold 3.jpg
 
One thing to realize, a 25 inch F/5 provides amazing views but observing with one is an effort, it takes energy, my 16 inch is way easier...
 
Jon
 
Edit:  It probably worth posting this photo that shows the relative sizes.  Left to right, 25 inch F/5 Obsession, 22 inch F/4.4 Starsplitter, 16 inch F/4.4 Dobstuff, 12.5 inch F/4.06 Jstar. 
 
4 Dobs plus Jon.jpg

 

 

 


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#9 Allan Wade

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Posted 17 January 2020 - 08:56 AM

I do believe it's an F/5, perhaps unfortunately!

I take my son on the star party circuit around the world, and we keep running into 25" f/5 Obsessions. I can not convince him that they are smaller dobs than my 32". He just looks at that focuser miles up in the sky and is convinced it's a bigger scope. 

 

1. Expectations

A 25" f/5 is a seriously serious scope. A 25" with good optics will deliver so much incredible observing.

 

2. Observing Practices

Leave it packed away in strong winds.

 

3. Accessories/Essentials

A very, very good ladder.

 

4. Transportation/Storage

Do not contemplate trying to transport the scope. Set it up somewhere permanently and enjoy it.

 

5. The possibility of astrophotography through it?

What are these strange ideas.


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#10 a__l

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Posted 17 January 2020 - 09:02 AM

A very, very good ladder.

 

Alas. I'm used to my 24"
This ladder 25" f/5 was enough for me for 1 hour, after which I migrated to Obsession 18" f/4.5 (the same with the ladder, but smaller).


Edited by a__l, 17 January 2020 - 09:25 AM.

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#11 Jon Isaacs

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Posted 17 January 2020 - 09:10 AM

5. The possibility of astrophotography through it?

What are these strange ideas.

 

 

There is a guy doing A-P with a 25 inch F/5 Obsession and a Tom O Platform but I think one is better off with a smaller scope on a GEM.

 

https://www.cloudyni...on#entry8535099

 

Jon



#12 bikerdib

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Posted 17 January 2020 - 09:16 AM

My advice; the scope will be too large.  It will give views so bright it will damage your eyes forever.  I suggest you change the delivery address and ship it directly to me, I'm willing to save you and take on the risk of eye damage.

 

Seriously!!

 

In all honesty, I'm envious.  You are getting my dream scope.  Congratulations, I'm sure you will really enjoy spending time with it.  Clear skies.


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#13 Ihtegla Sar

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Posted 17 January 2020 - 03:13 PM

Congratulations!  They don't make big wood telescopes with wood UTAs like that any more, so it's a real collector's item.  I have been keeping my eye out for one on the classifieds but the only ones that come up for sale are thousands of miles away and no one wants to ship anything that big.  You are definitely lucky to be getting one. 

 

The largest telescope Obsession currently makes in the Classic Design is 20" and from the sounds of it the whole Classic line will be going the way of the dodo bird soon because they don't sell as well as the UC design.  But there is something about the aesthetic of the Classic Obsession that I find compelling.

 

My only advice is at f/5 you may want to consider a coma corrector at some point but it is not necessarily right away.  I'd get used to the scope first.  But at some point you may want a coma corrector.  I have a 12" f/5 and its fine without a coma corrector but does show noticeable improvements towards the edge of the field with a coma corrector.

 

Good luck with your new scope and definitely do be careful up there on the ladder!



#14 Keith Rivich

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Posted 17 January 2020 - 04:01 PM

I do believe it's an F/5, perhaps unfortunately!

No. Not unfortunately. Its a great scope. The f/5 makes tolerances so much easier to deal with and getting to high magnifications with a wider field eyepiece is a joy. 

 

My only real suggestion is to not let setting it up and taking it down become a chore. If it becomes a hassle you will not use the scope. Make it part of the overall experience. My 25" only takes about 30 minutes to set up and 15 to tear down. Collimation is done in 10 minutes or less. Mirror is cooled down by the end of this process. 

 

As Tom says above use it and enjoy!



#15 Achernar

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Posted 17 January 2020 - 06:38 PM

Expect everything to look very different than through your previous telescope. A 25-inch Dob is a beast, it would be to your advantage to have a dark site to use it at, because light pollution pretty much negates the advantage of a huge aperture. You might want to keep it in a trailer, but watch out for dewing and make sure you have a secure place to store the telescope and or leave the trailer with the telescope inside. Get a good fiberglass ladder, metal ladders get cold on the hands, wooden ladders are heavy. Digital setting circles are well worth the money, even more so if you can connect it to a tablet or lap top. That way you can locate literally millions of objects. If you haven't bought them yet, start acquiring a set of high quality eyepieces and a coma corrector. A telescope like this really is worth using the best eyepieces you can get. Plan on going to some start parties at dark sites, you will get a chance to unleash your Dob under very dark skies. Above all, enjoy yourself and have fun! You can observe every night for the rest of your life, without ever coming close to seeing literally everything a 25-inch can show you.

 

Taras


Edited by Achernar, 17 January 2020 - 06:39 PM.


#16 Jon Isaacs

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Posted 17 January 2020 - 11:00 PM

Get a good fiberglass ladder, metal ladders get cold on the hands, wooden ladders are heavy.

 

 

The only fiber glass ladders I have seen are step ladders.

 

Based on my experience with my 25 inch F/5, a scope this big is poorly served by a step ladder. Metal ladders made from tubing can be insulated using pipe insulation, the same stuff people use to cover truss poles.

 

Jon



#17 CHASLX200

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Posted 18 January 2020 - 09:16 AM

That would be a killer scope in my seeing on planets.  Just no way my house is built for it and i would never use it.



#18 junomike

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Posted 18 January 2020 - 09:45 AM

Enjoy it for the killer views and use the C925 for AP.



#19 Jon Isaacs

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Posted 18 January 2020 - 10:35 AM

Enjoy it for the killer views and use the C925 for AP.

 

:waytogo:

 

When I sold my 25 inch, the guy who bought it happened to have a C-11 in his van. He asked me if I minded if he setup the C-11 for comparison purposes. I told him I had no problem with it but that I was sure after one look through the 25 inch, he would realize no comparison would be needed.

 

He spent the night with the scope and the next morning he told me I was right. He told me that in the 25 inch, m79, the magnitude 7.7 globular in Lepus, looked like M13 did in the C11.

 

If you do the math, that's just about right.

 

Jon



#20 tommm

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Posted 18 January 2020 - 11:51 AM

A 25" Obsession Classic is a big heavy scope.  You will need a van, pickup truck, or trailer to haul it, and check overhead clearance if the truck has a camper shell.  You will need ramps to load it in and out of the truck or van, and maybe the trailer (might have its own). Trailers are bouncy. I prefer a truck.  Don't make the ramps too short or you will have difficulty pushing it up them due to the weight of the scope. Try to limit the items you have to take to make it easier. Make a list, and check it each time so you don't forget anything.

 

Having said all that, the views will be amazing in dark skies, and well worth the effort to transport it to them. Near or in a city just doesn't compare. The more you do it the easier it will seem to you because it will become habit, familiar and easier to execute because you are used to it.  Leaving it sit for a long time between moves makes it seem more difficult. It will also be less difficult if you are younger - don't be put off by the geezers here telling you it is too difficult (I am one so I can say that - and I am still transporting a 22.4").

 

If it seems a chore moving it yourself, go with, or meet, someone else from a local astro club, a friend, or go to star parties.  The company and conversation will make set up and take down less tedious.  If you can, you might camp overnight. Then you can take the scope down in the morning after you've had some coffee.  Have fun and enjoy the views!


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#21 Jon Isaacs

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Posted 18 January 2020 - 03:41 PM

To address Tommm's comments:

 

A 2004 Nissan Frontier:

 

5615350-Obsession in back of Frontier.jpg
 
A Ford Transit Van:
 
Obsession sold 1.jpg
 
Obsession sold 2.jpg
 
obsession sold 3.jpg
 
Jon

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#22 jtsenghas

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Posted 18 January 2020 - 04:31 PM

It probably worth posting this photo that shows the relative sizes.  Left to right, 25 inch F/5 Obsession, 22 inch F/4.4 Starsplitter, 16 inch F/4.4 Dobstuff, 12.5 inch F/4.06 Jstar. 

Thanks,  Jon.  I need to see that photo from time to time to avoid getting overly ambitious in my builds. My 16.5" f/4.5 mirror I have squirreled away should suffice for my ultimate scope. 


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#23 tommm

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Posted 19 January 2020 - 12:15 PM

Jon, that first photo is exactly what I had in mind. OP, notice you can't see the front of the altitude bearings in the photo. They likely barely clear the the shell when loading. And notice how much of the truck bed is taken up just by the rocker/mirror box of the scope, you still have ladder and other things to take. But it is doable, just roll it in, load the other stuff, check your list twice, and head off into the hinterlands for a fun night.  So many stars crowding the sky you have difficulty finding the familiar constellations.  Wow, so much more detail in spiral galaxies and nebula than you ever saw at home! So many things to see!  Set up your camp stove on the tailgate in the morning, have coffee and breakfast while you enjoy the view and peace and quiet. It doesn't get any better.


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#24 tommm

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Posted 19 January 2020 - 01:00 PM

Jon's photo reminded me I have this one of my old Classic Obsession style 22.4" scope:

 

Attached File  Scope loaded in truck.pdf   75.48KB   37 downloads

 

The aluminum star plate on the ramps and the "filler boards" between the tailgate and bed make a smoother surface to roll the scope over. The scope is pushed in against the front of the bed and straps run from the bed front corners around the scope to hold it there. Just clamp the star plate in a vise between two pieces of angle iron that have lengths at least the width of the star plate, get a big hammer and wack away until it is bent to the angle you want.  Then bolt them to the boards. Saw off the other end of the boards at the same angle for smooth loading/unloading.

 



#25 Jon Isaacs

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Posted 20 January 2020 - 06:15 AM

Tom:

 

In the years I had my 25 inch, I loaded it when I bought it, unloaded it at our place in the high desert the next day and I never transported it anywhere.  

 

If I had, I would have made ramps.  What you don't see in my photo is that the ramps were up against the concrete step in the garage floor so they couldn't slip.

 

Jon 




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