"Finding" Planets for Imaging

[Macavity]

<Begin Wibble>

It may have been "done to death" elsewhere or discussed
in a more general way re. visual observing / imaging. BUT:
How do you "find" the Planets you intend to image! Or,
more specifically, what finding  technique(s) do you use?!

At the moment, I basically KNOW it's going to take me a
LOOOONG time to center the Planet in the Image field!

My "Planetary" scope is a MAK150 f/12 f=1800mm which
I Barlow by 2x... This seems to give something sensible:

Jupiter is about 240 (3.75 micron) pixels across... the ZWO
ASI120MM is 1280 x 960 max field!  You do the math/s? 

But you ALL know what I mean! The challenge is to put a
planet in a field of dimensions measured in "Arc Minutes"!
So, how do you guys do it?!?!

Personally, l'm quite into "Electronic" Finders! For those
of you who appreciate something a little... Off-Beat:

Not easy to see (There is no telescope!) But I attach
my finders to the Mount / Dovetail Bar! At bottom
right C-type 50mm lens plus "Mini Security Cam"...

Slung *underneath* (via my "Witty" mount clone)
the Dovetail Bar a "Super-Sensitive" Watec Camera
with an (inherited) Pentax 135mm f/4 SLR lens!

There are a lot of surplus (quality!) Pentax-thread
SLR lenses, from 70's on, for Astro-Finder use...

</End Wibble>

P.S. Why would I mount a finder underneath the
scope? Frankly my MAK150 is a HEAVY old thing!
Adding finders even further off-axis doesn't HELP!   

[michael.h.f.wilkinson]

The simplest method to centre a planet on the chip is with a flip mirror.

Put an EP in the top 1.25" barrel, the camera in the other, centre the planet in the EP in the usual way with the mirror down, and flip the mirror up. Mine cost me 99 euro, and it was well worth it

[chiltonstar]

Using a 180 Mak with a 2x barlow, I use the SW flip-mirror with illuminated EP. After a bit of fiddling around on the Moon (because the flip mirror and barlow are not exactly centred with the ASI224), I now have the centre crosswires exactly aligned with the planetary image on the laptop screen, or if it's not visible, it is very close to the edge and can be moved into view.

Chris

[Macavity]

Hi Michael --  And thanks for that! 

I actually have a Flip Mirror! In the fullness of time
it may prove to be the "winner" in this contest?

So far it has had ONE outing (I need to practice)!
I sense the problem is in  doing *many* different
types of Astronomy with the same equipment?

[Macavity]

6 minutes ago, chiltonstar said:

Using a 180 Mak with a 2x barlow, I use the SW flip-mirror with illuminated EP.

Thanks Chris (too!). So the Flip Mirror is (anyway) quite a good idea!
Quite glad I invested in one after all! It's ALL comforting to know...  

A nearby MOON is quite a lot of help too!
 

[knobby]

I count the number of turns from EP focus to cam focus .

Carefully align finder with scope.

Take out EP,

Put cam in then wind the previous mentioned number of turns but add another 3 turns 

Why the extra 3 ? 

It puts planet out of focus enough to make it a nice big donut that's easier to find with gain up high enough.

Cheaper than a flip mirror !

[Macavity]

From personal experience, there is often a fair amount
of "play" between Finder eyepieces / Cams etc. I have
had a certain amount of (improved) success using the
Baader "ClickLock" adapter. Better than Brass Rings?

[michael.h.f.wilkinson]

1 hour ago, knobby said:

I count the number of turns from EP focus to cam focus .

Carefully align finder with scope.

Take out EP,

Put cam in then wind the previous mentioned number of turns but add another 3 turns 

Why the extra 3 ? 

It puts planet out of focus enough to make it a nice big donut that's easier to find with gain up high enough.

Cheaper than a flip mirror !

Didn't work on my SCT when it only had the standard focuser. It shifts the image all over the place. Might work with the R&P focuser I have, but the risk of nudging the scope so the image is off chip is huge.

[knobby]

Fair point ... I use the feather touch but it's still a challenge 

[michael.h.f.wilkinson]

I first got the Vixen flip mirror when I had an SPC900NC, which only had a 3.2 mm x 2.4 mm sensor, as opposed to the 4.8mm x 3.6mm sensor of the ASI120MC. Worse still, the larger pixel size of the SPC900NC meant I needed more barlowing (F/30 rather than F/20). The Vixen flip mirror was a breath of fresh air, and took away the frustration of finding planets.

[Macavity]

I have fitted an "Electric" Crayford type focusser to my MAK.
Not strictly needed, but it helps? Idem the Jovian/Saturnian
moons as focussing aids! The reassurance that it all can be a
TAD tricky? It's not "just me" etc. etc. I feel better now! 

One can better appreciate the efforts of others as well... 

[saac]

Chris, firstly what a really great thread topic, finding out how others do what I/we struggle with is always a good read.  Love your image of Jupiter and I'm studying your setup with the electronic finders with great interest. I'm keen to make more use of an electronic finder myself;  last season I had a with a wee bit of success using the Polemaster in an electronic finder role - I'm keen to get my money's worth out of it  

Jim

[CraigT82]

I used an extension rube with my cam so that the camera was parfocal with my 12.5mm reticle ep. Centre planet in crosshairs, remove EP, insert cam and Barlow, done! I also used baader 2" clicklock which helps with centering consistency. 

[chiltonstar]

Something worth adding perhaps. My flip mirror takes the camera directly on the rear port, and the centre of the chip then exactly aligns with the crosshairs on the EP, but if I want to add a barlow (just the lens element) or IR filter on the front of the camera, I've had to use the 1 1/4 nosepiece fitting for the camera (which has a screw thread in the front). This slightly off-centres the camera though which is why I've added a shim cut from teflon sheet around the nosepiece so that everything is centred.

Chris

[JamesF]

I have a flip mirror, but I stopped using it with my SCTs and Maks because it changed the focal length far more than I was happy with for planetary imaging.  Especially so when imaging using a mono camera and there's also a filter wheel in the optical train.  (For readers who weren't aware, the focal length of a Mak or SCT changes depending on the distance between the primary and secondary mirrors, so moving the primary mirror to achieve focus also changes the focal length.)

I'm usually using a barlow for planetary imaging, but before adding that I put a reticle eyepiece into the scope (without the diagonal) and centre the image of the planet in the field of view.  I don't really care about focus at this point -- it's fine even if the planet appears as a doughnut as long as I can centre it.  Then I add the barlow and centre again with the reticle eyepiece.  If I'm using a higher power barlow I might step up through lower powers first.  Or if I'm using an extension then I'll centre the image, add it to the optical train and centre once again.  By that point I can be reasonable confident of the image being on the camera sensor when I swap it for the reticle eyepiece and make my final adjustments to telescope alignment.  This worked for me even with a sensor as small as that on my SPC900 (though I don't think I ever tried that camera in anything bigger than my 127 Mak).

James

[Macavity]

Some great ideas / points above! Ithankyouverymuch. 

Ah, Jim (saac)-- We share similar entusiasms! (My sympathies maybe)
BUT I do like Electro-Finders! A hangover from Video Astronomy days.
It occured to me one day that there is no a-priori reason why finders 
cannot be attached to the mount and even HELP with overall balance!

Aside: Me? It never got on well with standard Guide Scope Rings re. the
reproducibility and stability! Finders are (inherently) never accessible?
So I am intrigued to see how CLOSE I can get to finding (planets?) with
a longish focal length camera lens + screw thread Alt-Az "Witty" mount!

It's that "final push" (re. finding planets) that is the greatest challenge. 
The "coaxial" methods... Flip Mirror etc. seem the preferred solutions!
Then again, as James (JamesF) notes, adding all this "stuff" to a "CAT"
(catadiopteric system) really does change the "opticals" quite a bit!  

Plenty of food for thought. Thanks again.

[chiltonstar]

9 hours ago, JamesF said:

I have a flip mirror, but I stopped using it with my SCTs and Maks because it changed the focal length far more than I was happy with for planetary imaging.  Especially so when imaging using a mono camera and there's also a filter wheel in the optical train.  (For readers who weren't aware, the focal length of a Mak or SCT changes depending on the distance between the primary and secondary mirrors, so moving the primary mirror to achieve focus also changes the focal length.)

I'm usually using a barlow for planetary imaging, but before adding that I put a reticle eyepiece into the scope (without the diagonal) and centre the image of the planet in the field of view.  I don't really care about focus at this point -- it's fine even if the planet appears as a doughnut as long as I can centre it.  Then I add the barlow and centre again with the reticle eyepiece.  If I'm using a higher power barlow I might step up through lower powers first.  Or if I'm using an extension then I'll centre the image, add it to the optical train and centre once again.  By that point I can be reasonable confident of the image being on the camera sensor when I swap it for the reticle eyepiece and make my final adjustments to telescope alignment.  This worked for me even with a sensor as small as that on my SPC900 (though I don't think I ever tried that camera in anything bigger than my 127 Mak).

James

Some interesting comments! I've just measured the distance from the back of my Mak to the chip using the flip mirror (16cm) cpd with using a normal diagonal (17cm to the focal point), so for me, there's little in it.

Chris

[JamesF]

If the length of the optical train works for you then yes, I think a flip mirror makes a lot of sense.  I don't use the diagonal when imaging and in my particular setup just having a barlow and filter wheel in the visual back, adding the flip mirror messed things up a bit.  Such is life

James

[JamesF]

It's just struck me (in case it wasn't clear from the above) that if I'm doing some planetary imaging across a series of nights, I don't move the focuser at all when I go through the visual steps of aligning the OTA on subsequent nights.  I leave it exactly as it was when the image was focused on the camera.  It's no problem to centre the out-of-focus image visually and by the time I switch to the camera I have something close to being in focus again so I don't end up faffing about so much.

James

[newbie alert]

23 hours ago, michael.h.f.wilkinson said:

Didn't work on my SCT when it only had the standard focuser. It shifts the image all over the place. Might work with the R&P focuser I have, but the risk of nudging the scope so the image is off chip is huge.

If using a planetary cam,turn up the gain to nearly max,also unfocused can give you a bigger guide..use a bigger frame size and once you have located the target use smaller and smaller frames until you get to the 640x480..then reduce the gain to your required setting..ROI to reduce the file size too..

When you do the star alignment also make sure the finder is spot on then the target won't be too far away

If using the standard focuser you will cause mirror shift..if you get a crayford you won't 

[michael.h.f.wilkinson]

16 minutes ago, newbie alert said:

If using a planetary cam,turn up the gain to nearly max,also unfocused can give you a bigger guide..use a bigger frame size and once you have located the target use smaller and smaller frames until you get to the 640x480..then reduce the gain to your required setting..ROI to reduce the file size too..

When you do the star alignment also make sure the finder is spot on then the target won't be too far away

If using the standard focuser you will cause mirror shift..if you get a crayford you won't 

As I mention, I already have a rack and pinion focuser, so a Crayford would not be an upgrade (ask Olly Penrice ). If your camera has a tiny chip to begin with (like the SPC900NC which has a 640x480 chip), your approach does not work. I do not do star alignment as the scope does not have go-to, mainly because that would have costed an arm and a leg when I bought it 21 years ago, and partly because I love star-hopping. We regularly have outreach events on the terrace outside our university observatory (weather permitting, we have one this evening). By the time the go-to crowd have their alignment sorted, I have already picked up half a dozen sources . Won't be too far away isn't effective when the sensor is a few mm across, even with gain cranked up. A flip mirror works every time, especially with a an EP with reticle. 

[newbie alert]

Sorry didn't see you had a R&P...just see the sct part..

So no goto, and take it you're imaging..are you taking single exposures or lucky imaging? 

Personally I didn't get on with the flip mirror and rather use the method above..

[michael.h.f.wilkinson]

1 minute ago, newbie alert said:

Sorry didn't see you had a R&P...just see the sct part..

So no goto, and take it you're imaging..are you taking single exposures or lucky imaging? 

Personally I didn't get on with the flip mirror and rather use the method above..

I use lucky imaging

 

[PeterCPC]

+1 FOR Flip mirror but it's also very helpful to have an illuminated reticule finderscope. Just make sure that it is acurately aligned with the main scope.

Peter

[Merlin66]

+2 for the ease of the flip mirror.