Meade 10" / f8 ACF [visual]

[josefk]

Not that i'm impulsive or anything but a recent fabulous session chasing galaxies in the spring sky brought home to me a) I really like finding and observing galaxies, b) opportunities for galactic observing [in the UK] are few and there's a big list of galaxies to get through in a finite number of new moon / spring evenings.

Though i have a nearly 8" Cassegrain and generally appreciate that to step up in capability in a  "wow" kind of way from that scope i would need to upgrade to 12 inches of aperture for a full magnitude of light grasp improvement, i am a bit limited in choice for a 12" OTA. I live in an apartment and if not on foot for GnG in a nearby park then i have to drive my kit to a local observing spot (in a short wheelbase Land Rover).

Those circumstances preclude Dobsonians of both tube and truss style - i'm not wresting a 12" or larger tube (and base) up and down 2 flights of stairs and nor do i fancy sharing my office space at home with one day to day, i also don't fancy collimation (of a truss type) ahead of every session. Similar arguments rule out a large aperture newt unless it was very light and very fast and from what i read that sounds like a recipe for a floppy frustrating collimation nightmare :-(. 

So in my circumstances that leaves compound scopes.

Maksutov's i find quite interesting/appealing but large aperture ones are unobtanium, ££££, heavy and (from what i read) slow to cool. 

Large classical Cassegrain's are available (a design i like) but they're all heavy, some are v. expensive and the affordable ones have some funny design issues - i really would have liked one of the GSO 10" or 12" Classical Cass but they're both heavy, much bulkier than their mirror size suggests and for the 10" specifically, extremely tight regarding back focus if you would want to use 2" eyepieces (I calculated 2.7mm back focus 'margin of error' for TV EPs with a focal plane above the shoulder of the eyepiece and that is using the shortest focuser i could find and the shortest 2" diagonal i know of). They are also very long in focal length but still with quite large CO despite that focal length.

So finally SCT. My least favourite type of scope conceptually - very difficult to work up excitement for spending money on simple mirrors and float glass - no offence SCT owners 😆 i am one now (sort of - the Meade ACF isn't a vanilla SCT).

So, long story short, this weekend i have added this 10" Meade ACF to my observing toolbox with the principle target of big galaxy grabs per season:

 

Why Meade and not a Celestron (e.g. C11)? - i like the blue tube , HD radius blocks and HD losmandy 🙂, more controversially i like where Meade are made.

Why 10" and not 12" for the full magnitude upgrade? - I did have a 12" ACF in my hands for a few days and it was physically very manageable (better than i was expecting) BUT the one i had in my hands had a bit of an issue and had to be returned to the vendor, it was a one off reduced price type deal and i couldn't/can't bring myself to really splash out on a 12" at full retail price (mirror snobbery).

Why f8 and not the more sensible f10 seeing as i will use it purely visually? Well, i hope i haven't made a mistake i live to regret here. The CO of the f8 is massive (i haven't measured it for a percentage yet) but my thinking is...

• i don't need this scope to be a jack of all trades scope - apart from looking for fainter moons than i've found with 7" and looking for a bit of colour on Jupiter and Saturn i will hardly ever point this scope at a planet so any loss of planetary low level contrast is not a deal breaker,
• the f8 gives me maybe 1.2 degrees at the wide end and nearly 4mm of exit pupil for use with UHC and O-III for any nebula objects that fit in the 1.2 degrees (its difficult to get more than a degree and 3mm exit pupil out of the f10),
• i get a really great spread of exit pupils between 1.25mm and 2mm with existing eyepieces. My skies are typically SQM 20.5 and i know that around 1.3...1.5mm is a nice dark sky and a productive "faint fuzzies" (sp. galaxies) exit pupil range in my skies,
• counter intuitively (for me) the f8 has a flatter field than the f10 because there is less difference in the curve of the two mirrors and SCT field curvature comes from the difference in curvature between primary and secondary mirror not their compound focal length per se,
• the f8 has a really nice dual speed focuser - even messing about pointing through the kitchen window at a few distant pylons and with everything stood on a bouncy floating floor i can tell that this focuser only needs a light touch.

Nice 2-speed focuser (smooth):

 

So, why bother (with 10") at all when i have the 7.x" CC? - though i love the CC it bugs me that it is undersized vs the understanding i had when i bought it.  i like to follow lists (e.g. for 8" scopes) and it jars my OCD that mine is an odd size. More seriously because it's a bit undersized I will still be getting a circa 35% level of "betterness" with the 10" Meade. i can take this as ~35% more exit pupil at a given scale or 35% more scale at a given exit pupil. I know I see this improvement quite meaningfully because iv'e been testing this delta with existing kit.

Finally, mounting - here the AZ100 is just magnificent. I bought it with kit evolution in mind and here it is nonchalantly shrugging off about 28kg of dual mounted loveliness - it is'nt even balanced up properly here but i can tell already it doesn't care:

no SGL favoured lilckable objectives here i'm afraid but the float glass is nice: 😜

 

Edited April 28 by josefk
delete spurious picture

[josefk]

A few key stats - it annoys the hell out of me this stuff isn't readily available generally on manufacturers websites so - in case it's of use:

• Weight of the OTA - dust cap still on a Baader click lock already added: 15.5kg
• Length (to the back edges of the click lock/focuser: 58cm
• Diameter: 30.7cm
• Height e.g. largest dimension including Losmandy and guide scope "shoe" (e.g as would be needed for a bag or case choice): 37.5cm
• Circumference (e.g for a dew shield): 94cm
• Circumference (largest dimension around the Losmandy and guide scope "shoe"): 105cm

I'll add CO when i've measured it.

 

Edited April 28 by josefk

[ST_Steve]

Interesting choice, will be looking forward to your first light report…

[bosun21]

Nice addition to your stable. I look forward to your thoughts on the performance of the f8.

[magnahrl]

Also looking forward to your first light!

Magnus A.

[josefk]

12 hours ago, ST_Steve said:

Interesting choice, will be looking forward to your first light report…

I hope "interesting" doesn't turn out be a prophetic euphemism Steve 😂

Edited April 29 by josefk

[ollypenrice]

I bought a used one years ago for galaxy imaging, a project which was hi-jacked by the arrival of a TEC 140, so I've only ever used it visually. What can I say? It's very good on small targets like galaxies. I can't fault it.

Olly

[josefk]

59 minutes ago, ollypenrice said:

I bought a used one years ago for galaxy imaging, a project which was hi-jacked by the arrival of a TEC 140, so I've only ever used it visually. What can I say? It's very good on small targets like galaxies. I can't fault it.

Olly

If this gets out several sessions a year and nets me ~50 galaxies per season (more would be better but i know where i live) then it will earn its keep Olly. 

[ST_Steve]

2 hours ago, josefk said:

I hope "interesting" doesn't turn out be a prophetic euphemism Steve 😂

Just piqued my curiosity and genuinely looking forward to your thoughts.

I’m happy with my 8” CC including all its foibles and have no intention of replacing (currently 😂).

[mikeDnight]

I enjoyed following your reasoning and am batting for you, (I like Meade blue too!). I hope the 10" is everything you hope it to be. The massive central obstruction did make me "EEK!" out loud though. 

[John]

We have a 12 inch Meade ACF in our society observatory. I've not used it myself but those that have (primarily the imagers) seem pleased with it.

 

[josefk]

29 minutes ago, mikeDnight said:

I enjoyed following your reasoning and am batting for you, (I like Meade blue too!). I hope the 10" is everything you hope it to be. The massive central obstruction did make me "EEK!" out loud though. 

You might hear an "EEK!" out loud in Sth Lincs if i've misjudged this - possibly followed by something slightly stronger..."EEK!!!*%$£@!" 🙂 

[magnahrl]

Sounds like a good idea with a 10" f/8 "shorttube" SCT on a really good alt-az, like Rowan AZ100 for observing DS. Instead of a traditional dob. Especially if you have to walk down and up a couple of stairs.

You did not consider a standard C11 + 6,3 focal reducer? I have a C8 and I often use it with the FR, like it   -two scopes in one👍

Cheers,

Magnus A.

Edited April 29 by magnahrl
forgot a letter in my name

[josefk]

I did “do the maths” on it @magnahrl - both the standard C11 and the Edge11. 
For me there were points that counted against both in my “checklist”. 

It’s a great pity that astro shows and even astro shops are not open at night so they can do demos. I’m in an Astro club but it’s too far away for me to turn up at their observing nights (and their location is worse than mine) so no chance to grab a peek through someone else’s kit there either. 

I think a lot of us make the best analysis we can on paper then we have to “suck it and see” for better or worse. It’s why I find exchanging info on here so useful. 

 

[Xsubmariner]

I have the 12” f8 ACF and my initial intention was for a dual use setup, imaging and observing, hence I fitted an electro hydraulic pier. Unfortunately due to very limited clear skies, I am reluctant to disrupt the camera setup to use it for observing (I am not worthy).  While slightly soft, It works well for imaging galaxies. M94 captured last week, 1.5 hours total integration.

Edited April 30 by Xsubmariner

[josefk]

nice @Xsubmariner - did you ever use your 12" visually before you dialled in your imaging gear? I assume you have it permanently mounted? Any dew management tricks you want to pass on? 🙂 i'm probably going to wrap my OTA this week with a dew band under the insulation towards the front of the OTA. I'm waiting for a dew shield and when that comes i will probably also add a 2nd layer wrap around the OTA and dew shield combined at each session...

[magnahrl]

Xsubmariner...indeed works well for imagening galaxies. That picture of M94 is just wonderful👍Thanks for sharing!

/Magnus A.

[Xsubmariner]

Josfk, I had some limited visual experience before finalising the camera and Nightcrawler focuser settings, and  the visual image is excellent as you would expect. I have dewshield with integrated heater that I use with a controller.

I tried an additional heater strip around the OTA but it wasn’t needed as the shield heater was sufficient. The dew protection worked well last winter, you can see the frost on the flexible shield but the inside was clear.

[ollypenrice]

22 hours ago, magnahrl said:

Sounds like a good idea with a 10" f/8 "shorttube" SCT on a really good alt-az, like Rowan AZ100 for observing DS. Instead of a traditional dob. Especially if you have to walk down and up a couple of stairs.

You did not consider a standard C11 + 6,3 focal reducer? I have a C8 and I often use it with the FR, like it   -two scopes in one👍

Cheers,

Magnus A.

For visual you can open up the FOV as far as the baffle tube will allow without a focal reducer: you just need a longer FL eyepiece, I think?

Olly

[josefk]

Outstanding looking set-up @Xsubmariner - there's no wonder you don't want to break it down now for a visual peek! Wowser. ...and never mind the scope what a fabulously capable looking mount.

I have an Astrozap dew shield on back order and will probably receive a kendrick dew band and Pegasus dew controller today.

[josefk]

Yes I do also wrap the Xmas presents in our house 🙂

[bosun21]

1 hour ago, josefk said:

Yes I do also wrap the Xmas presents in our house 🙂

I bought a roll of aluminium tape at the same time as my reflectix.  The black looks good as well though 🤔. Where are you fitting the dew strip? Inside the insulation or outside?

Edited May 1 by bosun21

[josefk]

If it works @bosun21 then it may get a bit of aluminium tape as well as a treat. Actually I already did take a crafty look at gold foil on Amazon for a tongue in cheek JWST type look 🤣

 
I have a good dew band inside here (under this insulation) a few cm back from the font glass. This insulation is foiled backed camping mat. Foil on the outside. 
 

I have an aluminium dew shield on back order so when that is fitted that and the front of the tube will also get a layer (temporary - I.e. each session) of car windscreen foil shield or “reflectix” type material. Till the dew shield arrives I will just use a wrap of reflectix as the actual dew shield. 
 

I feel like I have crossed some kind of rubicon with this OTA. 

[ST_Steve]

4 hours ago, josefk said:

I feel like I have crossed some kind of rubicon with this OTA. 

It would seem that threshold has been reached 😂

Much more manageable than the large CC’s by the looks, what’s it like to mount up? Not sure if a handle would be nice (if possible to add)?

[josefk]

it was easy so far @ST_Steve - there is a handle on the back plate (doesn't really show in the pics) that is very convenient - it could do with a complimentary one at the front end for a two handed lift. I may look at adding something on the Losmandy if it feels a bit treacherous/slippy in the dead of night when cold and sleep deprived...

It's keeping me busy and i haven't looked through it in the dark yet!