Originally Posted by Apodidae49
Shot a dozen or so with it, had VC on 1 and AF on and it found focus very quickly but some of the 600mm shots were blurred as I was only shooting hand-held, sitting in a chair. However I also had some pin sharp shots. It was very dull so had ISO on 800 and was getting around 1/125th shutter at f6.3 so I suppose at that zoom and aperture the depth of field was virtually non-existent.
Totally different animal to anything Iíve ever used before. HEAVY, but I suppose in the grand scheme of things, itís a lightweight.
Iím going to sit back, take a breath and decide if a big lens is really for me or do I just want to increase my interest in general photography as the Nikon is head and shoulders above the LUMIX FZ72 in everything but reach.
First, I'd go shoot what you have, the d5600 + 70-300 AF-P. At 450mm without cropping (equivalent) you should be able to get some good stuff, especially if you can crop maybe 2x - 3x more. If you can shoot at a good ISO (say ~400 max) with fast shutter, you should be able to crop a lot. The lower the ISO, the better the cropping.
For a cropped 300mm, you still need to keep the shutter speed up because the apparent blur in the photo will depend on the cropped image. So try to stay up in the 1/640 - 1/1250 range (1/ (300 * 2) - 1/(300 * 4) range as you would crop). Faster is almost always better, assuming you have the light for a suitable aperture and ISO.
If you are shooting stationary subjects with decent support, you can always try lower shutter speed and see how well the VR kicks in. As you saw with the Tammy, even at 1/125 you can now and then get a sharp image. But it will not be consistent and only for stationary subjects not too far away.
The 70-300 AF-P VR only has a VR on/off mode. It does not have a "sports" or "panning" mode, so I'm not sure how well it will do trying to track BIF. But it sounds like you shoot from a hide with bean bag or similar support, so might not be an issue. You can only turn the VR on/off via a menu setting, there is no switch on the lens. Make sure it is set correctly.
The Aperture can open up wider compared to 600mm because 300mm has much better DoF . Your lens is f/6.3 at 300mm, so I'd shoot that mostly wide-open unless the subject is very close. A 300mm on DX sensor (CF 1.5) at f/5.6 at 60ft has a 2.7 ft (+/- 1.35 ft) DoF (18.3m is 0.82m), which is plenty for most birds unless you want wing-tip to nose on a side shot. A 600mm lens is only 0.66 ft (8" or 0.2m) so only +/- 4" (0.1m). That's why I shoot 600mm at f/8 is to get 12" or 0.3m of DoF. When I'm shooting larger birds (large hawks, heron, egret, etc.) I'll go f/10 to f/11 if I can, at 600mm.
In terms of the 150-600 test, I think you were in very low lighting. ISO 800 @ 1/125, f/6.3 is an EV value of, respectively, -3 +7 +5 1/3 = 9 1/3 which is like "night sports" or the dim end of "just after sunset." .
To have a good depth of field (say f/8) and good speed (say 1/1250) and reasonable ISO (say 400), you need a subject luminance of 14 1/3 EV, which is "hazy sunlight (soft shadows)" or the bright side of "just before sunset." Because it is a log-2 scale, that's 2 ^ (14 1/3 - 9 1/3) = 32x more light than what you were shooting in. Depending on situation, I sometimes pop up to ISO 800 - ISO 2000 or shoot at 1/1600 or 1/2000. I almost never shoot wider than f/8 for a 600mm lens (I think Chosun uses f/7.1 at 550mm).
Because all these numbers are usually too much to track while shooting, several of us have recommended the M setting (fixed speed and aperture) plus auto-ISO, where you can set your ISO limits (say 100 - 3200). The camera will show you a red ISO value of 3200 if it cannot make the lighting work, otherwise the ISO value will show in white. If I am shooting against a bright background (e.g. BIF), I will add a +0.7 to +1.0 EV exposure compensation, which tells the auto-ISO to make things brighter.
Note that EV calculations do not depend (directly) on focal length, only the f-stop (which depends on focal length).
, calculating DoF has a lot of factors and can vary a fair bit based on the sensor, so these numbers are guidelines and you might want to increase the f-stop a bit for more detail or decrease it for more blur.