Pushing it?

[LewisM]

I have a 5.7kg refractor enroute to me. I use a 1.5kg CCD, and maybe another kg if I use guidescope setup. That's 8.5kg.

The GPD2 I have now is rated to 10kg. Most say this is a photographic/conservative limit, but if it isn't, is 8.5 on a 10kg mount going to be pushing the realm of good tracking etc for imaging?

I love this mount, been perfect from day one, and I have had some awesome tracking and guiding with it. I have had it for sale in the hope of getting a Tak NJP, BUT now thinking do I even need to?

Yeah, I know no such thing as over-mounting, but I feel I just dont need to change anything. Thoughts?

[MattT]

I know nothing about cameras and photography in general BUT isn't it all about balance?
There is a refractor in the ol US a 6" f15 that the RA's motor was recycled from a cassette recorder....balance.
Am I close? Just my thoughts FWIW
Matt

[Larryp]

I had my TSA120 on a GPD2. Total weight about 9Kg for visual, and it handled it comfortably.
Guess you can only try it!

[RobF]

99% of the time these arbitrary limits people cook up are about minimising frustration and lost frames. Even the chinese gear that's available these days can take fantastic images as long you take the time to learn the strengths and weaknesses of the gear and work with it. Getting a decent number of frames and processing well makes an incredible difference to the final product.

So, should be fine really at those sorts of FLs would be my 2c.

[raymo]

I think that your GPD2 will handle it comfortably. I had a 6" SW Mak with
DSLR, 8x50 finder, and Telrad on my smaller Super Polaris, and it was quite happy.
raymo

[LewisM]

It is an f/6.4 system (it is NOT a TSA).

I know the mount WELL, it performs impeccibly, so I am inclined to keep it and use it

[RB]

LOL Lewis, you're always push'n it.

:P

[cometcatcher]

For photography probably be okay but not in any sort of wind. Visual use is less critical. For visual the balance can be kept neutral. For photography a slight loading of the RA axis to make the motor work a little more is desirable to prevent backlash. But you probably knew that anyway.

[LewisM]

Τι νέα έχεις;

:p

[LewisM]

790mm tube, on a mount weighted down additionally with 6kg counterweight in the accessory tray and a STIFF dec axis... won't move much :) I have imaged in some good wind with this mount and a LONGER f/9 scope - nada.

I "load" the RA and Dec - dec get's camera heavy (just to make sure IF my PA isn't perfect that at least Dec is ot suffering BL), and RA get's loaded depending on which side the scope is.

I'd love to update to the SXD2/SXP/EM200/NJP, but family circumstances just stopped that so will make the best of what I have (FINALLY!)

[cometcatcher]

:rofl: Don't believe you. :P

[beren]

Sorry man but got to say it all these scope's you have brought and there's a beauty of a mount {NJP} in the classifieds that could dismiss all the worry about carry capacity..........mount first scope later :)

[LewisM]

I know, just can't do it financially now

[garymck]

Hi Lewis,

I have a TSA120 currently mounted on an IEQ30 which is similar in size to a GPD2. The scope weighs about a kg or so more than your 102, and is about the same length, so I imagine my experience will be similar to yours.

My scope is acceptable, but not great on this mount. I fitted the mount to my CPC1100 tripod (since that scope is observatory mounted). On this tripod damping time is about a second and a half. Focusing at under 100x is easy, over this there is movement that makes focusing progressively more tedious as mags go up, though still doable at 300x.

I have yet to put my st8300c on the scope, but my impressions are that you will have to guide using an OAG, as a separate guidescope will be too much extra load.

I really believe this class of mount is excellent with shorter scopes like vc's, sct's small refractors etc. With that sort of scope my mount can take integrations of any length. Ideally I would want something bigger. Like you I advertised my mount for sale, but I only received ridiculous low ball offers.

If it had sold I would have unhesitatingly gone for a bigger mount. I have learned that longer scopes need bigger mounts.....

FWIW
cheers
Gary

[LewisM]

Gary,

Thanks but the scope is NOT a TSA102, rather, it is an FCT-100 fluorite triplet - Tak only made around 78 or so of these (latest guesstimate - I am still awaiting Tak to respond to my archival request), as they were so prohibitively expensive to produce.

The scope is the SAME size as the FSQ-106 and 106N (NOT the ED, EDX or EDXIII) - not surprising considering the FCT-100 gave birth to the FSQ-106 (which was cheaper and easier to make). It weighs in at 5.7kg, which is 1.3kg lighter than the FSQ-106EDXIII, and only 1.7kg heaver than the FSQ-85.

Only 1 FCT series model remains in production - if you can call on a custom basis only, and for HUGE $$$ - the FCT-250: http://www.takahashi-europe.com/en/FCT-250.php

I have considered my options, and BOTH mounts I have SHOULD handle it. My guidescope is a converted Tak 7x50 finder with helical focuser, and weighs less than 500g all up.

Be close, but I think it can do it.

[strongmanmike]

Get the NJP, I coooould be wrong I guess and I think you have seen it before but...something tells me you wouldn't be able to load up like THIS (http://www.pbase.com/strongmanmike2002/image/141334067/original) and get THIS (http://www.pbase.com/strongmanmike2002/image/141334127/original) with a GPD2 :question: ;)

Mike

[Shiraz]

yep, get the NJP.

To put it in perspective, consider the attached PE curve from http://daventura.xoom.it/daventura/strumenti_vixen/graficoPE_GPD2.jpg. That little hiccup at 400 seconds has about the same peak-to-peak error as the total PE (whole cycle) of an NJP (or even an EQ8 for that matter). The GPD2 is good for it's size, but it is not in the same league as the bigger mounts.

[LewisM]

That is NOT a happy GPD2. Never seen a curve anything near that with mine - I did see it with an HEQ5 once though!

Last time out, I had an RMS of 0.07 (see: http://www.iceinspace.com.au/forum/showthread.php?t=126628), varying by VERY little over a 10 minute period. That was with a 7.2kg rig. I have since readjusted Dec (was backlash), so next time out, fingers crossed.

I am going to convince myself the GPD2 can do it :)

[rmuhlack]

do you mean the black HEQ5, or the white one... ;)

[LewisM]

Black. Dec motor failure

[Shiraz]

I thought that PE curve looked pretty good - reasonably smooth and consistent. Not much published data on the mount, but found one other source suggesting 25 arcsec PE, which would be fairly similar. The point that I was making is that, apart from lower load rating, small mounts have a lot more PE to guide out than big mounts - and there is always a little bit left after guiding. Reducing PE is one of the main reasons why top end mounts have extra large worm wheels and bearings.

If you are measuring 0.07RMS (I presume that is in guide pixels), and guessing that your guide scope/cam has pixels of about 6 arcsec, your guiding is within about 0.4 arcsec RMS. That is pretty good - provided that you do not have guide settings such that the guide graph is flat, but at the expense of big stars. If your mount can reliably keep within 0.4 arcsec RMS, it will do the job.