Wenlock Basin City Road
19 Augt 1841
A letter <1> appeared in the Literary Gazette <2> of the 10th July last addressed by you to the Editor <3> of that Journal on the subject of Photography and as your name and address is appended to it I take the liberty of soliciting some further information on the subject
You state that Professor Petzval <4> of Vienna has invented a new combination of achromatic lenses in order to make the whole aperture useful – Each of the achromatic lenses has an aperture of one and half inch diamr and both act together with their full apertures as a single achromatic lense [sic] of five and half inches focus – The diameter of the image in its greatest distinctness is more than four Inches – you also state that you have constructed a camera obscura, in which there are two similar achromatic lenses, the distance between which can be increased or diminished at pleasure – This you state gives a very good effect, because it may be so managed as nearly to unite all the chemical rays into one focus –
On reading the above I was immediately struck with the advantages of the arrangement and constructed a camera which I expected would have produced the desired effect (a horizontal section of which I have enclosed) in this I was disappointed – I find it does not give a distinct field of more than about one and quarter Inch [sic] instead of four inches, and in taking a portrait with it although I can get the eyes, nose, and mouth very distinctly yet the hair & dress is always otherwise which of course I attribute to the want of a larger distinct field moreover I do not appear to gain any advantages by moving the glasses which I believe must arise from my not understanding how you manage them so as to unite all the chemical rays into one focus – I know I must fail in the management of the camera as I produce very good portraits with a small French camera with a glass one and threequarter Inch diamr and five and half inches focus – You I am confident will see at a glance how I have failed and I doubt not will readily give me the information I require and thereby greatly oblige
Your very obdient [sic] servant
H. W. Treffry<5>
[diagram of lettered section through camera, with key as follows:]
a, a' Two achromatic lenses each having an aperture of 1½ Inch × 10¾ Inches focus with the convex side towards the object, these lenses when nearly close together are equal to 5½ Inches focus – I have also tried two achromatic glasses each 8 Inches focus at various distances apart from four Inches to ¼ Inch with a similar result
b. A brass tube 2¼ Inches diamr in which the glasses a, a' with their cases slide at pleasure
c. Frame containing the ground glass which is replaced after the focus is set by another containing the plate
d, e. The two parts of the camera which slide one into the other to regulate the distance between the plate and the glasses
H. F. Talbot Esqr
Laycock Abbey <6>
2. The Literary Gazette and Journal of belles lettres, science and art.
3. William Jerdan (1782–1869), editor of The Literary Gazette.
4. Joseph Petzval (1807–1891).
5. Although Treffry has yet to be positively identified, in June 1842 the partnership was dissolved of William Treffry, William Henry Treffry, and Samuel Bevan, of Wenlock Basin, City Road, London; engineers, boiler makers, and iron founders. The daguerreotypist might have been a son or brother, or perhaps an intentional inversion of William Henry's name.
6. Readdressed in another hand.