30 replies to this topic

[patindaytona]

Trying to adjust to my new 16". I know that somewhere around 35 or 40 per inch of aperture is supposed to be about right for viewing planets etc due to seeing conditions, but I'm finding that it's really hard to even get a planet in view and when it is it drifts so fast by the eyepiece! I calibrate my telrad and finderscope once I find it but even then seems just a fingertip nudge and it's out of view. 

I guess this is part of the game but what do others here use for magnification on planets with a 16" It's a f/4.5 by the way.

[Redbetter]

Whatever the seeing will support for the aperture you have is "about right for viewing planets" and it varies with the night and conditions.  At 16", 35x/inch is 560x.  That is awesome if you have the seeing for it, but that sort of seeing s rare nearly everywhere.  Daytona might have extremely good seeing on average though.  With the 20" and local seeing, anything past 278x is rarely productive for planetary locally, better nights will allow 357x and very rarely 400+.  When I lived in East Texas, I used from 500 to 700x for planetary at times with the 20" while sketching Mars...so location matters.  When I lived there I was accustomed to seeing Jupiter's moons as steady disks...which nearly never happens here (can't recall the last time.)

 

Nagler fields of view are what I find the sweetspot at f/5.  More field than that and coma would be out of my comfort zone and I would want to have a Paracorr.  An f/5 will have ~37% more coma than f/4.5 and I doubt I would be happy with a Nagler without a Paracorr.  If I had a Paracorr I would be using Ethos type fields for high power with the 20".  That would be expensive of course...and the extra field is limited by the 1.15x factor of the Paracorr, but it would be sharper throughout the outer field.  

 

The mechanics of the mount matter.  You need smooth enough motion that you can nudge it along at 300 to 600x.  I hand track with the 20" at higher magnification than that for some very tight double stars and resolving asteroids as non-stellar--in spite of the local seeing.  I have a lot of weight on the UTA of my 20" so it is not the smoothest in motion, but I can deal with Plossl fields even at those mags as needed.

[RodgerDodger008]

On my manual dob wider fov eyepieces made a big difference to what you describe but also using less magnification or a combination. Rest is just practice practise practise imo.

[krishnak]

In my seeing conditions for planets, I use 260x which is 7mm eyepiece with my ES 16 inch telescope. Sometimes lesser down to 10mm eyepiece. This is almost half the magnification what you are able to try/target in your conditions.
I start centering my RACI finderscope (with cross hairs) with the eyepieces starting from GSO 2 inch 30mm, then 21-7mm svbony. After I reach 7mm, I swap in the AT 7mm UWA and reacquire the target using the finderscope. Thanks.

[Vic Menard]

...I know that somewhere around 35 or 40 per inch of aperture is supposed to be about right for viewing planets etc...

That might be true for a small refractor.

And for a large Newtonian, that might still be true for separating double stars.

But resolving surface detail on planets can be tricky, and typically requires a sharper, brighter image. 

In my observing experience with 16- to 22-inch apertures (with laminar, coastal Florida skies), when the seeing permits, I find the optimal image size for studying planetary surface detail is somewhere between 20X to 25X per inch of aperture (to make the image twice as large would be 40X to 50X perch of aperture). This assumes good optics, the cooling glass/scope has settled down, the collimation is within the prescribed tolerances, and the target planet is at least ~45-degrees above the horizon. Even then, the image quality may fluctuate if there are more than a few people surrounding your scope.

 

That said, I get very nice views of Saturn and Jupiter at 320X (about 15X per inch of aperture).

 

... I'm finding that it's really hard to even get a planet in view and when it is it drifts so fast by the eyepiece!

Even at 15X per inch of aperture, an Ethos eyepiece would be a good investment (followed by a Paracorr).

I use both (Ethos and Paracorr), and my scope is driven.

 

For what it's worth, before I moved up to a driven Dobsonian, I had a "push to" 20-inch f/6.2 Tectron Dobsonian that I manually tracked, often from the top of an 8-foot ladder! I used that scope for almost a decade, and I can assure you that, with practice, you will find that it gets easier to both center a planet in a 300X field of view and to keep it centered, even with a crowd waiting for a turn at the eyepiece. 

[Kitfox]

Vic, did that 20" Tectron nest like my 15" does?  I love the advantage at 15", not sure how practical that is for the 20". 

 

On topic, please tell us what dob you have, Pat.  Lots of options to improve the ease of tracking, I'm sure there are some improvements we can all make...

[miguel gonzalez]

Can you read:

https://www.cloudyni.../944027-saturn/

 

I like to get in future APM/AT 5 mm XWA.

[CowTipton]

Trying to adjust to my new 16". I know that somewhere around 35 or 40 per inch of aperture is supposed to be about right for viewing planets etc due to seeing conditions, but I'm finding that it's really hard to even get a planet in view and when it is it drifts so fast by the eyepiece! I calibrate my telrad and finderscope once I find it but even then seems just a fingertip nudge and it's out of view. 

I guess this is part of the game but what do others here use for magnification on planets with a 16" It's a f/4.5 by the way.

35-40x per inch is too high on most nights around here (suburban Chicago area.)

Just go as high as your seeing supports, make sure your mirror is acclimated to the outside temperature, and make sure your collimation is as perfect as you can get it.

 

Most nights with my 14" I can get around 15-20x per inch.  On very good nights I can get around 30x per inch.

 

 

Wider AFOV eyepieces can keep your object in the field of view for a longer period when manually tracking but you'll have lots of coma to deal with unless you're using a corrector.

Here is the difference between an 11mm 82° eyepiece and an 11mm 50° eyepiece in my scope with the coma corrector:

 

 

MUCH, much wider which gives the planet a lot more time to traverse the FOV at the same magnification.

Edited by CowTipton, 03 December 2024 - 10:53 AM.

[Redbetter]

With regard to Vic's experience, my first views of M51 through a 22" Tectron (IIRC) as a novice were what convinced me that going up in aperture (from my 8" SCT) was more than worth doing.  (Not slighting the 8" SCT here, I got a lot out of it for planets and DSO's for years after that, as well as before.)   Most importantly, I asked the owner of the big scope to wait a few minutes so that I could bring my wife over.  After she looked through the eyepiece she said, "okay, you can buy your big scope."  I waited several years for a foreign assignment to pay for the scope outright, along with some stock market gains to fully pay for the truck that hauls it around.   I still use both as my main astro gear.

 

FWIW, her saying I could purchase the scope wasn't so much of a yes/no as "I'm fully behind you doing this."  She wouldn't have objected to me doing what I wanted (that isn't the way we operate in either direction), but after looking through the big scope she fully understood why I recognized I needed to go bigger.

[patindaytona]

Vic, did that 20" Tectron nest like my 15" does?  I love the advantage at 15", not sure how practical that is for the 20". 

 

On topic, please tell us what dob you have, Pat.  Lots of options to improve the ease of tracking, I'm sure there are some improvements we can all make...

ES 16" F/4.5   I had been using a 12" for several years and decided to buy the 16" even though I live in light polluted skies. I searched everywhere pros and cons alike what a difference it would make. Another topic, but i do use a night vision intensifier so I can really see a difference vrs the 12". I'm just getting used to the 16' and am doing lots of comparison's and tests with it mostly.

Can someone give me an answer to a question that's been very hard to resolve.  Comparing my 16" f/4.5 (1826mm f.l.) side by side with my 12" f/4.9 (1500mm f.l.) will the 16 have more magnification for a given eyepiece?     I don't know if it being a faster scope would somehow lower magnification.
 

Edited by patindaytona, 03 December 2024 - 11:56 AM.

[patindaytona]

Can you read:

https://www.cloudyni.../944027-saturn/

 

I like to get in future APM/AT 5 mm XWA.

Good info thanks
 

[Vic Menard]

Vic, did that 20" Tectron nest like my 15" does?  I love the advantage at 15", not sure how practical that is for the 20".

The 20 was a custom setup (even the Galaxy Optics mirror was a "one off" using the cast iron tool for a 25-inch f/5 to grind the 20-inch f/6.25 mirror surface). To improve the altitude function, the altitude trunnions were full capture (3 pieces of teflon for each contact point) to effectively "lock" the mirror box to the rocker box (even Walter Scott Houston was impressed with the overall stability and ease of (manual) tracking).

 

It was indeed a nested design, but after a year or so of ownership and having to load the heavy complete nested box into the back of my van, Tom Clark and I sawed off the bottom 6-inches of the mirror box (about 60 pounds of wood, glass, and mirror cell parts) and set it up with spring latches and handles so it could be easily removed for loading and unloading the rest of the nested scope. A custom top to fit the 6-inch mirror box provided safe storage.

[Kitfox]

The 20 was a custom setup (even the Galaxy Optics mirror was a "one off" using the cast iron tool for a 25-inch f/5 to grind the 20-inch f/6.25 mirror surface). To improve the altitude function, the altitude trunnions were full capture (3 pieces of teflon for each contact point) to effectively "lock" the mirror box to the rocker box (even Walter Scott Houston was impressed with the overall stability and ease of (manual) tracking).

 

It was indeed a nested design, but after a year or so of ownership and having to load the heavy complete nested box into the back of my van, Tom Clark and I sawed off the bottom 6-inches of the mirror box (about 60 pounds of wood, glass, and mirror cell parts) and set it up with spring latches and handles so it could be easily removed for loading and unloading the rest of the nested scope. A custom top to fit the 6-inch mirror box provided safe storage.

 

I just noticed your address...that has to have been a cool experience!  Where did that scope go?

 

ES 16" F/4.5   I had been using a 12" for several years and decided to buy the 16" even though I live in light polluted skies. I searched everywhere pros and cons alike what a difference it would make. Another topic, but i do use a night vision intensifier so I can really see a difference vrs the 12". I'm just getting used to the 16' and am doing lots of comparison's and tests with it mostly.

Can someone give me an answer to a question that's been very hard to resolve.  Comparing my 16" f/4.5 (1826mm f.l.) side by side with my 12" f/4.9 (1500mm f.l.) will the 16 have more magnification for a given eyepiece?     I don't know if it being a faster scope would somehow lower magnification.
 

 

Magnification will be higher with a given eyepiece on the 16"; simply, magnification = objective FL / Eyepiece FL.  Speed of the scope is not part of the calculation.

[Vic Menard]

I just noticed your address...that has to have been a cool experience!  Where did that scope go?

The last I heard, Canada...

[patindaytona]

I just noticed your address...that has to have been a cool experience!  Where did that scope go?

 

 

Magnification will be higher with a given eyepiece on the 16"; simply, magnification = objective FL / Eyepiece FL.  Speed of the scope is not part of the calculation.

An f/4.5 would have a wider FOV than the F/4.9    That does not affect the magnification somehow even though the 4.9 has longer f.length?
 

Edited by patindaytona, 03 December 2024 - 03:35 PM.

[briansalomon1]

Trying to adjust to my new 16". I know that somewhere around 35 or 40 per inch of aperture is supposed to be about right for viewing planets etc due to seeing conditions, but I'm finding that it's really hard to even get a planet in view and when it is it drifts so fast by the eyepiece! I calibrate my telrad and finderscope once I find it but even then seems just a fingertip nudge and it's out of view. 

I guess this is part of the game but what do others here use for magnification on planets with a 16" It's a f/4.5 by the way.

I'm using a 15" f4 and get to some very good seeing at high elevations. With everything on my telescope just right, I use 375X and 475X (25X to 32X per inch) and get a lot of detail on planets. My telescope has a 2" thick primary, and without a vibrationless fan blowing onto the front of the mirror it won't go past 275X regardless of the seeing/elevation. https://www.cloudyni...811-12000-feet/

 

There is a lot that goes into getting 30X to 40X per inch out of a dob, but I would say the main two are seeing and mirror cooling. Most people probably don't have the seeing to support it.

 

As others have said, getting your telescope's movements to respond smoothly is important. Using a very wide angle eyepiece helps quite a lot.
 

[rjacks]

Yes, you have to adjust your planetary magnification based on seeing conditions, drift time across the field of view, the smoothness of motion of your scope, and your experience with hand guiding.

 

I have a hand-guided 16" f/4.5 dob, and if I am looking at planets, I start at 210X. If that looks very good, I go to 300X. Where I live, seeing conditions are very rarely good enough to go beyond that. If seeing conditions are good, you can pick up a lot of detail in Saturn and Jupiter at 300X.  With a 70 degree AFOV, drift time at 300X is fairly relaxed. If you want to magnify planets beyond that without a tracked scope, you will have to shell out for the 100 degree AFOV eyepieces. 

 

If the planets don't look good at 210X, I give up on planets for that night and go to objects for which poor seeing isn't very important. 

[RodgerDodger008]

An f/4.5 would have a wider FOV than the F/4.9 That does not affect the magnification somehow even though the 4.9 has longer f.length?

Magnification is focal length divided by mm on the eyepiece (eyepiece focal length)

Focal ratio which is focal length divided by aperture does not change the maginification.

Aperture does affect the theoretical usefull magnification.

But yes if the f4.9 has a longer focal lentgh the maginifcation would be higher but not because of the higher f number.

Example only:
F4.9 at 1000mm fl vs a f4.5 at 1000mm fl with a 10mm eyepiece would both give exactly 100x magnification. In this example the the f4.9 would be 222mm aperture and the f4.5 would be 204mm aperture. The max theoretical mag on the f4.9 would be 444x and on the f4.5 it would be 408x. In reality due to seeing 300x is prob the max under excellent conditions and around 200x in most conditions.

Edited by RodgerDodger008, 03 December 2024 - 06:02 PM.

[CrazyPanda]

I guess this is part of the game but what do others here use for magnification on planets with a 16" It's a f/4.5 by the way.

 

With my 14.7" operating at F/5.3, I typically top out at 280x magnification, but sometimes seeing is good enough for 330x. On very rare nights I'll go over 400x, but those are like once every couple of years type of nights.

 

When seeing is not so good, I'm usually floating around 200x. If seeing can't even support 200x cleanly, I don't bother with the planets.

[Keith Rivich]

Get tracking. You will not be disappointed...

[CHASLX200]

Trying to adjust to my new 16". I know that somewhere around 35 or 40 per inch of aperture is supposed to be about right for viewing planets etc due to seeing conditions, but I'm finding that it's really hard to even get a planet in view and when it is it drifts so fast by the eyepiece! I calibrate my telrad and finderscope once I find it but even then seems just a fingertip nudge and it's out of view. 

I guess this is part of the game but what do others here use for magnification on planets with a 16" It's a f/4.5 by the way.

Coma city kitty at F/4.5 so needs a Paracorr.  If motions are jerky it will make high pow wow's not so fun to use.  But i can tell ya this if it is a top notch made scope like a Starmaster or Obsession with a Zambuto like mirror i would have no prob using 1000x+ on my best nites. Hand tracking at 1000x is not easy in any Dob. But 450x to 600x should be fine if ya got the seeing.  Most times 250x to 350x is the norm. Not sure where you live.

[vtornado]

Besides seeing there is also exit pupil.  To see detail the retina needs to be well illuminated.   You have a 400mm mirror.  400x gives a 1mm exit pupil.  Go below 1 mm and the object starts dimming out for me. My personal limit is .8mm exit pupil. 400 / .8 = 500x.  I'm sure personal biology has a role.

 

For tracking, centering.   Try an optical finder with cross hair.  A zoom eyepiece can be zoomed out, if you lose the planet.

My dob tracks easier if I use two hands to turn it, one on the box, the other on the tube.  Assuming the majority of the motion is in azimuth, work on getting your azimuth bearings smoother.  Some folks use turtle wax.  I have also used WD40.

Edited by vtornado, 03 December 2024 - 09:27 PM.

[Mike Q]

I have done 400x on planetary a few times with my 16 inch, but it is a rare thing to be able to get that high more then once or twice a year.

[CHASLX200]

I have done 400x on planetary a few times with my 16 inch, but it is a rare thing to be able to get that high more then once or twice a year.

You would love it here before sunup in the summer.  OInly time i ever look at planets is in the AM as my seeing is always bad at sundown.

[Mike Q]

You would love it here before sunup in the summer.  OInly time i ever look at planets is in the AM as my seeing is always bad at sundown.

I spent two months in Florida in 1985....in August and September.  Thanks but i will gove Florida a pass lol